Method for monitoring and controlling the coolant temperature of a drive device of a separator

Abstract

A method for controlling the coolant temperature of an electric motor of a drive device (8) of a rotor of a centrifuge, preferably a separator (1) with a vertical axis of rotation, more particularly during execution of a centrifugal separation of a suspension into at least two different product phases; wherein the rotor has at least one rotatable drum (2), and wherein the drive device has an electric motor (8) that directly or indirectly rotates the rotor, and wherein the drive device also has an apparatus (100) for supplying the electric motor with a coolant and the apparatus comprises a control apparatus, has at least the following steps: a) providing the centrifuge with the drive device; b) driving the rotor, more particularly during execution of the centrifugal separation of a suspension into at least two different product phases; by means of the electric motor, and c) cooling, in a controlled manner, the electric motor at least during step b) in cooling cycles interrupted by breaks.

Description

[0001] Method for monitoring and controlling the coolant temperature of a drive device of a separator

[0002] The invention relates to a method for controlling the coolant temperature of an electric motor of a drive device of a rotor of a centrifuge according to the preamble of claim 1.

[0003] In order to achieve a compact design for centrifugal separators of this type, the drives of these separators are equipped with an integrated, water-cooled electric motor for direct drive of the rotor with the separator drum.

[0004] It is known that the coolant must be provided in the required quantity and within the permissible temperature range for cooling the electric motor, as specified by the electric motor manufacturer. This allows the maximum permissible motor temperature to be maintained. The required flow rate is limited, for example, by a suitable orifice or needle valve.

[0005] An additional opening valve opens the coolant supply when the electric motor is running and closes it as soon as the electric motor is switched off. The opening valve for the coolant is permanently open during drive motor operation, and the coolant flows through the drive motor at a flow rate specified by the electric motor manufacturer.

[0006] With this approach, coolant consumption remains constant, regardless of the drive motor load (product throughput, discharge frequency, and discharge size) as well as the actual temperature of the incoming coolant. State-of-the-art solutions have therefore been developed to address this problem.

[0007] DE 38 09 149 C1 describes that the cross-section of the coolant drain line can be changed step by step depending on the coolant drain temperature of a drive unit (engine).

[0008] DE 20 2007 004 983 U1 describes that water cooling is used as a circuit arrangement to cool centrifuge drives, which necessitates a circulation pump and a heat exchanger. EP 00 16 584 A1 describes that water cooling is also used to cool centrifuge drives, which is fed to a heat exchanger.

[0009] State-of-the-art concepts for cooling electric motors in separators have proven successful in practice. The disadvantage of these concepts is that coolant consumption remains quite high.

[0010] The object of the invention is to solve this problem.

[0011] The invention achieves this object by the method of claim 1 .

[0012] A method is provided for regulating the coolant temperature of an electric motor of a drive device of a rotor of a centrifuge, in particular of a separator with a vertical axis of rotation, in particular during a centrifugal separation of a suspension into at least two different product phases; wherein the rotor of the centrifuge has at least one rotatable drum, and wherein the drive device has an electric motor which directly or indirectly rotates the rotor, and wherein the drive device further has a device for supplying the electric motor with a coolant, which device comprises a control device, the method comprising at least the following steps: a) providing the centrifuge with the drive device;b) driving the rotor with the electric motor, in particular during the centrifugal separation of a suspension into at least two different product phases and c) controlled cooling of the electric motor at least during step b) for a limited cooling phase in cycles interrupted by breaks.;

[0013] It can further preferably be provided that the calculation of the length of the cooling phase of a respective cycle is carried out by the control device taking into account one or more measured values, wherein the at least one measured value or the several measured values ​​can be temperature measured values.

[0014] By cooling in cycles, coolant consumption is generally significantly reduced compared to continuous cooling. In a cooling system constructed in the manner of a circuit, a reduced coolant volume per unit time can be used, or less coolant is circulated. According to a particularly advantageous variant, the cycles of step c) comprise the following substeps: c1) Opening an opening valve of the coolant supply system to generate a flow of coolant through a cooling fluid system of the electric motor, which has at least one coolant supply line and one coolant discharge line, as well as an engine coolant passage;c2) Measuring an instantaneous temperature of the coolant Tmom after a predetermined time tmess has elapsed at the coolant outlet by a temperature measuring device and transmitting the measured value for Tmom to a control device, wherein the predetermined time tmess is determined as a function of a length of the coolant outlet between the electric motor and the temperature measuring device; c3) Comparing the measured value of Tmom with an upper limit value of the coolant temperature Tgrenz; c4) Calculating a time tcooling by the control device as a function of Tmom, during which time the opening valve additionally remains open; c5) Closing the opening valve after tmess and tcooling have elapsed for a cycle pause time tpause^ whereupon the method steps c1) to c5) are repeated almost endlessly in the manner of a program loop after tpause has elapsed until the operation of the centrifuge drive motor has ended.

[0015] This results in the following total cycle time: tcycius = tmess + tcool + tpause

[0016] This creates a method for monitoring and controlling the coolant temperature of a centrifuge, allowing the current coolant temperature to be kept as constant as possible at a defined upper coolant temperature limit. This allows the separator's electric motor to operate at the maximum permissible temperature and with the lowest possible coolant consumption, regardless of its load, the ambient temperature, and the temperature of the incoming coolant.

[0017] A further advantage of the method according to the invention or of a separator with a correspondingly equipped control device is that it is easy to retrofit to existing coolant-cooled electric motors, since in terms of hardware, essentially only the temperature measuring device on the coolant outlet needs to be added. A temperature sensor within the electric motor is not required, although it can be provided. Furthermore, only a simple valve with two switching positions ("open" and "closed") is required as the opening valve. Therefore, no control valve or an adjustable iris diaphragm, nor multiple valves and lines, as in prior art solutions, are required.

[0018] In addition, a computer program product is stored and executed on the control device or another memory that is or can be connected to it, which computer program product comprises instructions that cause the method steps of the method for cooling the electric motor to be carried out in cycles, in particular the method steps according to one of claims 1 to 14, on the separator for cooling the drive device.

[0019] According to a particularly preferred embodiment of the invention, the opening valve is closed immediately after the time period tmess when the instantaneous coolant temperature Tmom is below an upper limit of the coolant temperature Tgrenz. This allows the coolant to absorb thermal energy up to a defined upper limit temperature for the coolant, thereby advantageously reducing the required coolant volume flow.

[0020] According to another particularly preferred embodiment of the invention, the opening valve remains open for a further time tcooli when the instantaneous coolant temperature Tmom is greater than or equal to the upper limit of the coolant temperature Tlimit. This lowers an elevated coolant temperature to a defined upper limit temperature for the coolant, while simultaneously advantageously minimizing the required coolant volume flow.

[0021] Furthermore, according to another particularly preferred embodiment of the invention, an assignment table of the measured values ​​of Tmom and tcooling is determined experimentally, resulting in a centrifuge-specific or coolant supply system-specific characteristic curve that represents the relationship between Tmom and tcooling, so that coolant temperature control is designed as a type of characteristic curve control. This results in an advantageously simple operating principle of the coolant control, which can be individually adapted to the respective separator.

[0022] Alternatively, according to a further particularly preferred embodiment of the invention, it can be provided that in step c) one or more measured values ​​of the current coolant temperature Tmom, and preferably additionally one or more measured values ​​of the ambient temperature and one or more current engine load parameters are fed to the control device - in particular a higher-level control device of the separator - whereupon the control device uses these measured values ​​to determine a cooling time tcool according to an algorithm. If the coolant temperature does not change in the desired direction after several subsequent cooling cycles, the algorithm is adjusted by the control device, preferably by the higher-level control device, until the coolant temperature is set to the value Tlimit.This adaptability of the algorithm allows the control system to adapt particularly advantageously to changing operating conditions.

[0023] Alternatively, according to another particularly preferred embodiment of the invention, a PID controller can be used as the control device. This advantageously allows for particularly flexible monitoring and control of the coolant temperature.

[0024] The invention can be used constructively in various cooling system variants.

[0025] Likewise, according to a further particularly preferred embodiment of the invention, it can be provided that the coolant supply system is designed according to the principle of a closed coolant circuit.

[0026] According to a further particularly preferred embodiment of the invention, it is provided that the coolant is pumped in the circuit by means of a pump and cooled by a heat exchanger and the required cooling capacity is supplied to the heat exchanger via a refrigeration circuit.

[0027] Furthermore, according to another particularly preferred embodiment, the coolant can be taken from a storage tank and, after flowing through the electric motor and absorbing heat, pumped back into the storage tank. This creates an open circuit to which coolant can be added or removed as needed. This is advantageous, for example, during short-term peak loads. This variant also effectively minimizes coolant consumption.

[0028] In this context, according to a further preferred embodiment, the heat absorbed by the coolant is released by convection through a wall of the storage tank to the surroundings of the storage tank. This effectively minimizes the potential coolant refill volume, thereby advantageously saving coolant.

[0029] It is particularly advantageous if the wall of the storage tank is equipped with suitable means to improve convective heat dissipation. This further effectively minimizes the potential coolant refill volume, thereby saving coolant.

[0030] The invention also provides a separator with a control device and further means adapted to carry out the steps of the method according to any one of the preceding claims. It also provides a computer program product comprising commands or instructions that cause the separator of claim 15 to carry out the method steps according to any one of claims 1 to 14. A computer-readable medium on which the computer program is stored is also provided.

[0031] Further advantageous embodiments of the invention can be found in the remaining subclaims.

[0032] The invention is described in more detail below using exemplary embodiments with reference to the drawing. The invention is not limited to these exemplary embodiments, but can also be implemented in other ways, either literally or in other equivalent ways. It shows:

[0033] Fig. 1 is a schematic sectional view of a separator with a coolant supply system for the drive motor;

[0034] Fig. 2 is a simplified circuit diagram of a coolant supply system for a separator;

[0035] Fig. 3 shows a variant of the coolant supply system from Fig. 2;

[0036] Fig. 4 shows a further embodiment of the coolant supply system from Fig. 2; and

[0037] Fig. 5 is a flow chart illustrating an exemplary method according to the invention; and

[0038] Fig. 6 is another flowchart illustrating substeps from Fig. 5.

[0039] Several exemplary embodiments are described in the following description of the figures. The individual features of these exemplary embodiments can also be combined with exemplary embodiments not shown and are also suitable as advantageous embodiments of the subject matter described in one or more of the main and subclaims.

[0040] Fig. 1 shows a centrifuge that can be designed as a separator 1. The centrifuge—here the separator—has a rotor. This rotor comprises a rotatable drum 2 with a vertical axis of rotation D. This drum 2 can be surrounded by a hood arrangement 3. Terms such as "top" and "bottom" refer below to the exemplary vertical arrangement of the drum 2. The drum 2 is placed on a drive spindle 4. This is rotatably mounted in a bearing housing 7 by a bearing arrangement, which here comprises an upper bearing 5 and a lower bearing 6. By way of example, this bearing arrangement has two roller bearings. Other configurations are conceivable (not shown here).

[0041] The separator drive comprises an electric motor 8 for rotating the rotor with the drum 2. This electric motor 8 comprises an electric motor housing 9 with a stator 10 or stator winding and a motor rotor or rotor 11.

[0042] The electric motor 8 advantageously does not have its own bearing, which allows for a more cost-effective design. Instead, the bearing arrangement is arranged here, for example, between the electric motor 8 and the drum 2. However, the bearing arrangement can also be implemented in other ways.

[0043] The drive spindle 4 can, for example, also be connected directly—that is, preferably without intermediary elements such as a coupling—to the rotor 11. The electric motor housing 9 with the stator 10, on the other hand, can be arranged rigidly and unsprung on the machine frame 12 of the separator 1 or can be supported thereon.

[0044] In this way, the drum 2 with the drive spindle 4, the rotor 11 and the bearing housing 7 form an oscillating unit which is elastically supported on the machine frame 12, but to which the stator 10 does not belong, so that relative movements occur between the rotor 11 and the stator 10.

[0045] The drive spindle 4 is arranged in a bore-like opening 13 of the single- or multi-part bearing housing 7 by means of the bearing 5 and the bearing 6. The bearing housing 7 has an upper flange 14 and a lower sleeve-like section 15, which passes through an opening 16 in the machine frame 12.

[0046] The upper flange 14 is supported on the machine frame 12 via circumferentially distributed elastic damping elements 17, which are distributed between the underside of the flange 14 and the upper side of the machine frame 12, wherein the flange 14 and the machine frame 12 are provided with ring-like steps 18, 19 in the area of ​​the damping elements 17.

[0047] Furthermore, a lubricant supply 20 can be provided to supply the bearings 5, 6 with lubricant.

[0048] The present description relates to an advantageous embodiment, but is not limited to this design. Rather, the coolant supply system described below and the associated methods can be used with the separator described above, but also with separators with a different design.

[0049] A centrifuge according to the invention - for example designed like the separator in Fig. 1 - has a coolant supply system 100 which supplies the drive or, in this case, its electric motor 8 with coolant. A fluid, in particular water, can be provided as the coolant. Other suitable fluids can also be used as the coolant. The coolant supply system 100 has at least one coolant supply line 101 - also called the coolant flow line - and one coolant discharge line 102 - also called the coolant return line. A motor coolant flow line 113 is arranged between the coolant supply line and the coolant discharge line and can be guided through elements of the electric motor and / or past these. This is where the actual cooling of the electric motor 8 takes place, here in particular the stator, which heats the coolant in this section. The coolant supply system 100 can have further elements, such as, for example, a cooling fan.B, one or more controllable valves.

[0050] Fig. 2 shows, in particular, elements of an exemplary coolant supply system 100 of a separator—e.g., separator 1 of Fig. 1. The coolant supply system 100 here again comprises the coolant supply line 101, the motor coolant passage 113, and the coolant discharge line 102, each of which is connected to the electric motor s. A controllable opening valve 103 can be provided in the coolant supply line 101. The opening valve 103 is designed to be controllable. It can preferably be opened and closed by a control device 105, controlled by an electrical or electromagnetic actuator. However, the opening valve 103 can alternatively also be actuated in another way.

[0051] The coolant discharge line 102 of the embodiment of Fig. 2 then has a temperature measuring device 104. The temperature measuring device 104 can be designed, for example, as a resistance temperature sensor. The temperature measuring device

[0052] 104 may also be configured in a different way. The coolant supply system 100 further comprises a control device 105. The control device

[0053] 105 can be designed as a standalone control device that only controls the coolant. Alternatively, it can also be integrated into a higher-level control device of the separator. It is designed to receive measured values ​​from the temperature measuring device 104. The temperature measuring device

[0054] 104 is connected to the control device 105 so that it can process the recorded measured values. The control device 105 is also designed to control actuators, such as the valve 103, directly or via interposed control means in the manner of a control device.

[0055] The control device 105 can comprise a microprocessor and interfaces, as well as additional control means connected in between, such as a gateway and downstream components, by means of which it can be connected at least to the controllable actuators, such as the opening valve 103, and to one or more sensors, such as the temperature measuring device 104. This connection can be made via a wired or wireless data transmission link.

[0056] The method described below is proposed for monitoring and controlling the coolant temperature of the drive of separator 1. This method actively controls the coolant volume flow flowing through the electric motor 8 of the separator drive.

[0057] For this purpose, it can be advantageous and simple to provide that the control device

[0058] 105, the opening valve 103 opens and closes in pulsed fashion during operation of the separator or during operation of the drive with the electric motor 8 used as the drive, wherein the duration of the opening pulse depends on the measured coolant temperature Tmom at the coolant outlet 102 of the electric motor, which is measured by the temperature measuring device 104. This procedure results in very low coolant consumption. Thus, it is often possible to achieve a reduction in coolant consumption compared to the specifications of the electric motor manufacturer and, for example, to sustainably reduce water consumption.

[0059] First, the centrifuge is prepared (with its drive) and the rotor is set in rotation with the electric motor 8, and the centrifugal processing is started (Fig. 5 - steps a, b).

[0060] During the rotation (from the beginning) of the rotor, the cooling also starts in cycles (Fig. 5 step c), whereby the sub-steps of this step c) can then be repeated continuously during the centrifugal separation (see Fig. 6).

[0061] At the beginning of each cooling cycle of the electric motor 8, which is in operation, particularly during centrifugal separation, and which rotates the drive spindle 4 of the separator 1, the opening valve 103 for the coolant supply to the drive motor is opened for a defined period of time tmess (Fig. 6 - step c1), whereby the heated coolant is forced from the motor coolant passage 113 (e.g., a cooling jacket of the electric motor 8) into the coolant discharge line 102, which also houses the temperature measuring device 104. This measures the instantaneous coolant temperature Tmom after the time tmess has elapsed and transmits this measured value to the control device 105.To ensure that the coolant temperature is measured correctly, the time tmess can be suitably selected depending on the length of the coolant discharge line 102 between the electric motor s and the temperature measuring device 104, based on empirical values ​​from previous cycles or other measured values ​​from comparable centrifuges. Depending on Tmom, the control device 105 calculates the additional time tcooling for which the opening valve 103 remains open.

[0062] If the measured value of Tmom is below an upper limit value of the coolant temperature Tgrenz (e.g. 40°C), the opening valve 103 can be closed again immediately after the period tmess.

[0063] If the measured value of Tmom is above the upper limit of the coolant temperature Tlimit, the opening valve 103 is opened further for the time tcooling.

[0064] A value or assignment table of the measured values ​​of Tmom and tcooling can be determined experimentally. This results in a centrifuge- or coolant supply system-specific characteristic curve that represents the relationship between Tmom and tcooling, so that the coolant temperature control is designed as a type of characteristic control. Alternatively, the measured values ​​of the current coolant temperature, possibly the ambient temperature, and possibly the engine load can be fed to the control device (105). The control device feeds these measured values ​​to a suitable algorithm that determines a cooling time tcooling. If the coolant temperature does not change in the desired direction after several subsequent cooling cycles, the algorithm is adjusted by the control device until the coolant temperature adjusts to the value Tlimit.This intelligent adaptability of the algorithm allows the control system to adapt itself particularly advantageously to changing operating conditions.

[0065] Alternatively, a PID controller can be used, which is configured accordingly so that a limit control is realized with a parameterizable controller, by which tkühi is calculated individually depending on Tmom.

[0066] After tmess and tcooling time have elapsed, the opening valve 103 remains closed for the cycle pause time tpause. The cooling cycle then starts again. The total cycle time tcykius is thus the sum of tmess, tcooling time, and tpause.

[0067] The respective cycle is thus simplified as follows and comprises the following sub-steps: c1) Opening the opening valve 103 of the coolant supply system 100 to generate a flow of coolant through a cooling fluid system of the electric motor 8; c2) Measuring an instantaneous temperature of the coolant Tmom after a predetermined time tmess has elapsed at the coolant discharge line 102 by the temperature measuring device 104 and transmitting the measured value for Tmom to a control device 105, wherein the predetermined time tmess is determined as a function of a length of the coolant discharge line 102 between the electric motor (8) and the temperature measuring device 104; c3) Comparing the measured value of Tmom with an upper limit value of the coolant temperature Tgrenz; c4) Calculating a time tcool by the control device 105 as a function of Tmom, during which time the opening valve 103 additionally remains open;c5) Closing the opening valve 103 after tmess and tcooling have elapsed for a cycle pause time tpause^, whereupon the process steps c1) to c5) are repeated "quasi-endlessly" in the manner of a program loop after tpause has elapsed until the centrifuge drive motor stops operating. Thus, process steps d) to c5) are repeatedly executed or repeated in the manner of a loop with the aid of the control device 105, preferably until the drive motor stops operating. The program is then aborted.

[0068] The aim of the coolant temperature control according to the invention is to keep the instantaneous coolant temperature Tmom as constant as possible at Tlimit (manufacturer's specification). In this way, the electric motor 8 is operated at the maximum permissible temperature and with the lowest possible coolant consumption, regardless of its load and the temperature of the incoming coolant.

[0069] The specifications of the electric motor manufacturer regarding the volume flow of the incoming coolant are usually static data for the rated load of the electric motor 8. For example, a volume flow of 3 l / min is specified at a maximum coolant temperature of 40°C and a rated load of 37 kW.

[0070] In practice, such an operating point almost never occurs without coolant temperature control. Either the electric motor 8 is operating at partial load and / or the coolant inlet temperature is lower than the maximum permissible.

[0071] Thus, more coolant is generally supplied to the electric motor 8 per unit of time than the operating situation of the electric motor 8 requires. The invention eliminates this deficiency in a simple manner.

[0072] A further advantage of this measuring and control arrangement is that it is easily retrofittable to existing coolant-cooled electric motors, since it only requires the addition of the temperature measuring device 104 to the coolant outlet 102. A temperature sensor within the electric motor 8 (e.g., in the coolant chamber) is not required. Furthermore, only a simple valve with two switching positions ("open" and "closed") is required as the opening valve 103. Therefore, no control valve or an adjustable iris diaphragm, nor multiple valves and lines, as in prior art solutions, are required.

[0073] In Fig. 3, the coolant supply system 100 is designed according to the principle of a closed coolant circuit. This achieves a further reduction in coolant consumption. For this purpose, the coolant is pumped in a circuit with the aid of a pump 106 and cooled by a heat exchanger 107. The required cooling power is supplied to the heat exchanger 107 via a refrigeration circuit 108. In a further embodiment of the coolant supply system 100 according to Fig. 4, the coolant is taken from a storage tank 109 and, after flowing through the electric motor and absorbing heat, is pumped back into the storage tank 109. The heat absorbed by the coolant is released again via a wall 110 of the storage tank 109 to the environment of the storage tank 109, primarily by convection. The wall 110 of the storage tank 109 can be equipped with suitable means for improving convective heat dissipation, such as cooling fins.If the heat capacity of the coolant in the storage tank 109 and the heat dissipation via convection are insufficient, coolant that is too warm can be drained via a first line 111 and cold coolant can be supplied via a second line 112.

[0074] The following application examples of the method according to the invention for monitoring and controlling the coolant temperature for the separator 1 show a significant coolant saving with a coolant-cooled drive motor - here designed as a three-phase motor - for example with these performance data:

[0075] Pout = 37 kW Pout = 40 kW

[0076] Coolant flow rate: 3 l / min (manufacturer specification) Maximum cooling water temperature: 40°C (manufacturer specification)

[0077] The parameters for the coolant control were as follows: tmess^ 2 see tkuhi: 2 see tpause: 6 see tzykius: 1 0 see

[0078] Test 1 : (Measurement after thermally stable operation) Load: 35.9 kW

[0079] Coolant inlet temperature: 23.1 °C Coolant outlet temperature: 40.8°C Coolant volume flow: 1.85 l / min Temperature increase: 17.7K

[0080] Test 2: (Measurement after thermally stable operation) Load: 26.3 kW

[0081] Coolant inlet temperature: 23.5°C Coolant outlet temperature: 40.9°C

[0082] Coolant flow rate: 1.73 l / min

[0083] Temperature increase: 17.4K It is shown that the coolant requirement can be advantageously kept low.

[0084] Reference symbol

[0085] 1 separator

[0086] 2 drums

[0087] 3 Hood arrangement

[0088] 4 drive spindle

[0089] 5 Upper camp

[0090] 6 Lower bearing

[0091] 7 bearing housing

[0092] 8 Electric motor

[0093] 9 Engine housing

[0094] 10 Stator

[0095] 11 runners

[0096] 12 Machine frame

[0097] 13 Opening

[0098] 14 Flange

[0099] Section 15

[0100] 16 Opening

[0101] 17 Damper element

[0102] 18 levels

[0103] 19 levels

[0104] 20 Lubricant supply

[0105] 100 Coolant supply system

[0106] 101 Coolant supply line

[0107] 102 Coolant drainage

[0108] 103 Opening valve

[0109] 104 Temperature measuring device

[0110] 105 Control device

[0111] 106 Pump

[0112] 107 heat exchangers

[0113] 108 Refrigeration circuit

[0114] 109 Storage tank

[0115] 110 wall

[0116] 111 first line

[0117] 112 second line

[0118] 113 Engine coolant line

[0119] D axis of rotation

Claims

Claims Method for regulating the coolant temperature of an electric motor of a drive device (8) of a rotor of a centrifuge, preferably of a separator (1) with a vertical axis of rotation, in particular during a centrifugal separation of a suspension into at least two different product phases; wherein the rotor has at least one rotatable drum (2), and wherein the drive device has an electric motor (8) which directly or indirectly rotates the rotor, and wherein the drive device further has a device (100) for supplying the electric motor with a coolant, which device comprises a control device (105), characterized by at least the following steps: a) providing the centrifuge with the drive device;b) driving the rotor with the electric motor, in particular during the centrifugal separation of a suspension into at least two different product phases and c) controlled cooling of the electric motor at least during step b) for a limited cooling phase in cooling cycles interrupted by breaks.; 2. Method according to claim 1, characterized in that the length of a respective cooling phase is determined by the control device (105) taking into account one or more measured values.

3. Method according to claim 2, characterized in that the length of a respective cooling phase is determined by the control device (105) taking into account one or more temperature measurement values.

4. Method according to claim 1, characterized in that the cooling cycles of step c) comprise the following sub-steps: c1) opening an opening valve (103) of the coolant supply system (100) for generating a flow of coolant through a cooling fluid system of the electric motor (8), which has at least one coolant supply line (101) and one coolant discharge line (102) as well as an engine coolant passage (113); c2) measuring an instantaneous temperature of the coolant Tmom after expiration of a predetermined time tmess at the coolant discharge line (102) by a temperature measuring device (104) and transmitting the measured value of the instantaneous temperature of the coolant Tmom to a control device (105), wherein the predetermined time tmess is dependent on a length the coolant discharge line (102) between the electric motor (8) and the temperature measuring device (104); c3) comparing the measured value of the instantaneous temperature of the coolant Tmom with an upper limit value of the coolant temperature Tgrenz; c4) calculating a time tkühi by the control device (105) as a function of the instantaneous temperature of the coolant Tmom, during which time the opening valve (103) additionally remains open; c5) closing the opening valve (103) after the expiration of the predetermined time tmess and the time tkuhi for a cycle pause time tpause; whereupon the method steps c1) to c5) are carried out again in the manner of a program loop after the expiration of the cycle pause time tpause until the operation of the electric motor ends.Method according to claim 4, characterized in that in step c5) the opening valve (103) is closed immediately after the time period tmess if the instantaneous coolant temperature Tmom is below an upper predetermined limit value of the coolant temperature Tgrenz. Method according to claim 4, characterized in that the opening valve (103) remains open for a further time tkuhi if the instantaneous coolant temperature Tmom is above the upper predetermined limit value of the coolant temperature Tgrenz. Method according to one of the preceding claims, characterized in that an assignment table of the measured values ​​of Tmom and tkuhi is determined experimentally, resulting in a centrifuge- or coolant supply system-specific characteristic curve that represents the relationship between Tmom and tkuhi, so that the coolant temperature control is designed as a characteristic curve control.Method according to one of claims 1 to 7, characterized in that a PID controller is used as the control device (105). Method according to one of the preceding claims, characterized in that in step c) the control device (105) is supplied with one or more measured values ​​of the current coolant temperature T mom, and preferably additionally with one or more measured values ​​of the ambient temperature and one or more current engine load parameters, whereupon the control device (105) uses these measured values ​​according to an algorithm. A cooling time tcooli is determined using a algorithm, whereby if the coolant temperature does not change in a desired direction after several subsequent cooling cycles, the algorithm is adjusted by the control device until the coolant temperature reaches the value Tlimit.

10. Method according to one of the preceding claims, characterized in that the coolant supply system (100) is designed according to the principle of a closed coolant circuit.

11. Method according to claim 10, characterized in that the coolant is pumped in the circuit by means of a pump (106) and cooled by a heat exchanger (107) and the required cooling power is supplied to the heat exchanger (107) via a refrigeration circuit (108).

12. Method according to one of claims 1 to 9, characterized in that the coolant is taken from a storage tank (109) and, after flowing through the electric motor (8) and absorbing heat, is pumped back into the storage tank (109).

13. The method according to claim 12, characterized in that the heat absorbed by the coolant is released again by convection to the environment of the storage tank (109) via a wall (110) of the storage tank (109).

14. Method according to one of claims 12 to 13, characterized in that excessively warm coolant can be drained from the storage tank (109) via a first line (111) and cold coolant can be fed into the storage tank (109) via a second line (112).

15. Separator with a rotatable rotor and with a drive device (8) comprising an electric motor for rotating the rotor, as well as with means adapted to carry out the steps of the method according to one or more of the preceding claims.

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