A method for measuring the ground resistance value in a temporary power system in a freezing station

Abstract

The present invention discloses a method for measuring the grounding resistance value of a temporary power supply system in a freezing station, comprising the following steps: S1 clearly determining the grounding resistance R of a transformer (1) in a front-stage substation supplying power to the freezing station; A , as known; S2 installs a short-circuit switch at the point where the L line enters the housing of the electrical equipment; S3 is in the freezing station, without repeated grounding or disconnecting the repeated grounding, closes the short-circuit switch, short-circuits the L line and the housing of the electrical equipment, and measures the voltage U of the housing of the electrical equipment to the earth t ; S4 is in the freezing station, and is repeatedly grounded; close the short-circuit switch, short-circuit the L line with the outer shell of the electrical equipment, and measure the voltage U between the outer shell of the electrical equipment and the earth t1 , the voltage U of the electrical equipment shell to the equipotential connection t2 ; S5 according to R A 、U t 、U t1 、U t2 Calculate the ground resistance R B The present invention can measure the load side grounding resistance in a relatively small freezing station without disconnecting the system power supply, disconnecting the grounding electrode and the grounding wire, or setting an auxiliary grounding electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply and distribution in a freezing station during freezing construction, and more particularly to a method for measuring the grounding resistance value in a temporary power system in a freezing station. Background Art

[0002] Freezing construction requires a safe, reliable, and stable power distribution system. The quality of the power supply plays a decisive role in the success of freezing construction. Currently, the basic grounding types in low-voltage power distribution systems include TN-C, TN-S, TN-CS, TT, and IT.

[0003] The TN-C system combines the neutral (N) and protective (PE) conductors of the entire system. While this saves one conductor, it offers a lower level of safety. For example, if the PEN line in a single-phase circuit is interrupted or poorly conductive, the metal casing of the equipment will carry a 220V fault voltage to ground, posing a significant risk of electric shock. RCDs cannot be installed to prevent electric shock and ground arc fires. The PEN conductor cannot be disconnected, making it unsafe for equipment maintenance. Neutral current flows through the PEN conductor, potentially interfering with information systems and electronic equipment during construction. For these reasons, the TN-C system is not suitable.

[0004] Because the PE conductor of the TN-S system does not normally carry operating current, its potential is close to the ground potential, which will not cause interference to information technology equipment and can greatly reduce the risk of electric shock or fire. It is particularly suitable for the following industrial and civil buildings:

[0005] (1) Civil buildings such as public buildings, hospitals, and residences that have high requirements for power supply continuity or protection against electric shock;

[0006] (2) Industrial plants and freezing station construction sites with large single-phase loads or large nonlinear loads;

[0007] (3) Places with many information technology systems and high electromagnetic compatibility (EMC) requirements, such as communication stations, computer stations, microelectronics plants, and scientific research, office, and financial buildings;

[0008] (4) Places with explosion or fire hazards.

[0009] The TN-CS system uses PEN conductors between independent substations and buildings, but the N and PE conductors are separated after entering the building. Its safety level is similar to that of the TN-S system. Therefore, it is suitable for electrical installations in buildings and places listed in item (2) above that are not equipped with distribution transformers.

[0010] The TT system is grounded separately from the power supply system grounding because the exposed conductive parts of the electrical device are grounded separately. The device casing is at ground potential and will not introduce ground fault voltage on the power supply side. The protection against electric shock is better than the TN-S system, but RCD must be installed. Therefore, it is also suitable for electrical installations in buildings and places listed in the above item (2) without distribution transformers. It is especially suitable for outdoor places without equipotential bonding, such as outdoor lighting, outdoor performance venues, outdoor markets, etc. It is especially suitable for electrical installations in freezing stations during freezing construction.

[0011] IT systems, with their minimal ground fault current and low fault voltage, avoid risks such as electric shock, fire, and explosion, ensuring maximum power supply continuity and safety. Therefore, they are suitable for locations requiring uninterrupted power supply and strict limits on ground fault voltage, such as emergency power supply systems, fire protection, underground mine electrical installations, hospital operating rooms, and other locations requiring fire and explosion protection. However, because they typically lack a neutral conductor, they are not suitable for powering single-phase loads such as lighting and control systems. Furthermore, the complexity of ground fault protection and maintenance limits their application in other locations.

[0012] The TN-CS system mentioned above is generally used at the construction site of the freezing station. Repeated grounding is often carried out at the construction site of the freezing station, and equipotential bonding is set up inside the freezing station. If it is necessary to measure the load side grounding resistance inside the freezing station at the construction site of the freezing station, it is necessary to disconnect the grounding electrode from the grounding wire and then use a grounding resistance meter to measure, such as Figure 1 As shown in the figure, according to the operating specifications, an auxiliary electrode is generally required to be set up 10 meters away from the ground electrode being measured, and a second auxiliary ground electrode is set up 20 meters away. However, the space in the freezing station at the construction site is limited, making it difficult to have sufficient space to complete the installation of two auxiliary ground electrodes. Therefore, measuring the load-side ground resistance in the freezing station at the construction site is cumbersome and difficult. Summary of the Invention

[0013] To this end, the technical problem to be solved by the present invention is to provide a method for measuring the grounding resistance value in the temporary power supply system of a freezing station, which can obtain the grounding resistance value on the load side of the freezing station construction site through live operation without disconnecting the system power supply, disconnecting the grounding electrode and the grounding wire, using a grounding resistance megohmmeter, or setting up an auxiliary grounding electrode.

[0014] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0015] A method for measuring the grounding resistance value in a temporary power system in a freezing station comprises the following steps:

[0016] S1 specifies the grounding resistance R of the transformer in the preceding substation that supplies power to the freezing station. A , as known;

[0017] S2 is equipped with a short-circuit switch where the L line enters the outer shell of the electrical equipment. The short-circuit switch has a function of automatically tripping after closing. The electrical equipment is located at the rear of the distribution box of the freezing station.

[0018] S3 is in the freezing station. Without repeated grounding or disconnecting repeated grounding, close the short-circuit switch, short-circuit the L line with the outer shell of the electrical equipment, and measure the voltage U between the outer shell of the electrical equipment and the earth. t , the short-circuit switch automatically trips after a delay;

[0019] S4 is in the freezing station and is repeatedly grounded. The grounding resistance is R B Close the short-circuit switch, short-circuit the L line with the outer shell of the electrical equipment, and measure the voltage U between the outer shell of the electrical equipment and the earth. t1 , the voltage U of the electrical equipment shell to the equipotential connection t2 ;

[0020] S5 is based on the known grounding resistance R A and the measured U t 、U t1 、U t2 Calculate the grounding resistance R according to the following formula B ,

[0021]

[0022] Furthermore, before step S2, the method further includes step S0: setting a protection switch at the power distribution box of the freezing station.

[0023] Furthermore, the short-circuit switch has a delay adjustable function, and the delay time is adjustable within 0-5s.

[0024] Furthermore, the protection switch has the functions of adjustable delay and operating current, and the delay time is adjustable within 0-5s.

[0025] Furthermore, the short-circuit current generated by the short circuit in step S4 is recorded as I d The short-circuit current generated by the short circuit in step S5 is I d ', then I d =I d '.

[0026] The technical solution of the present invention achieves the following beneficial technical effects:

[0027] The present invention can obtain the grounding resistance value on the load side of the freezing station construction site by obtaining the measured voltage through live operation without disconnecting the system power supply, disconnecting the grounding electrode and the grounding wire, using a grounding resistance megohmmeter, or setting up an auxiliary grounding electrode; the voltage measurement steps and the calculation steps are simple and easy to operate, and the invention can be applied to the measurement of the grounding resistance value on the load side of the construction site under conditions of insufficient space. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a wiring diagram of a TN-CS system in the prior art;

[0029] Figure 2 The measurement U of the embodiment of the present invention t Wiring diagram and equivalent circuit diagram when

[0030] Figure 3 The measurement U of the embodiment of the present invention t1 Wiring diagram and equivalent circuit diagram when

[0031] Figure 4 The measurement U of the embodiment of the present invention t2 Wiring diagram and equivalent circuit diagram.

[0032] The reference numerals in the figure are as follows: 1-substation transformer; 2-distribution box; 3-electrical equipment. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0034] like Figures 2 to 4 As shown in the wiring diagram, the house in the figure represents the construction site freezing station. The upstream substation transformer 1 that supplies power to the freezing station is outside the freezing station. The distribution box 2 and the power equipment 3 are installed in the construction site freezing station. The substation transformer 1 is grounded. The L line and PEN line are connected between the substation transformer 1 and the distribution box 2. The distribution box 2 is grounded via the grounding busbar. The power equipment 3 is connected to the distribution box 2 via the PE line. The power equipment 3 is located after the distribution box 2. In actual working conditions, there are usually multiple power equipment 3. The shorting switch is installed on the housing of the power equipment, which is the housing of the power equipment. Figures 2 to 4 The wiring diagram in FIG. 3 only schematically illustrates the electrical equipment 3 equipped with a shorting switch. U0 in the equivalent circuit diagram is the phase voltage of the transformer supplying power to the substation. The voltage used in the freezing station is generally 380V or 220V.

[0035] like Figures 2 to 4 As shown, a method for measuring the grounding resistance value of a temporary power supply system in a freezing station is characterized by comprising the following steps:

[0036] S1 specifies the grounding resistance R of transformer 1 in the preceding substation supplying power to the freezing station. A , as known; a protection switch is provided at the freezing station distribution box 2; the protection switch action characteristics match the switch in the previous substation, and the protection switch has automatic and manual reclosing functions;

[0037] S2 is equipped with a short-circuit switch where the L line enters the outer shell of the electrical equipment. The short-circuit switch has a function of automatically tripping after closing. The electrical equipment is located at the rear of the distribution box 2 of the freezing station.

[0038] In the freezing station, S3 closes the short-circuit switch without repeated grounding or disconnects the repeated grounding, short-circuiting the L line with the outer shell of the electrical equipment, generating a short-circuit current I d ,according to Figure 2 Connect a voltmeter to measure the voltage U between the housing of the electrical equipment and the earth. t , the short-circuit switch automatically trips after a delay;

[0039] S4 is in the freezing station and is repeatedly grounded. The grounding resistance is R B ; Close the short-circuit switch to short-circuit the L line with the outer casing of the electrical equipment, generating a short-circuit current I d ',according to Figure 3 Connect a voltmeter to measure the voltage U between the housing of the electrical equipment and the earth. t1 ,according to Figure 4 Connect a voltmeter to measure the voltage U of the equipotential connection between the housing of the electrical equipment. t2 ;

[0040] S5 is based on the known grounding resistance R A and the measured U t 、U t1 、U t2 Calculate the grounding resistance R according to the following formula B ,

[0041]

[0042] According to the calculated grounding resistance R B , can be used directly to determine the grounding resistance R B Whether the regulatory requirements are met;

[0043] Aiming at the difficulty of measuring the load-side grounding resistance at the freezing station construction site, the inventor of the present invention has proposed this measurement method through intensive research and design, integrating years of experience and research results in power supply and distribution at construction sites of related projects. The method only requires installing a short-circuit switch at a designated location to measure the grounding resistance of the load side. t 、U t1 、U t2 The three voltages can be substituted into formula (1) to calculate the ground resistance R BThis method does not require the installation of auxiliary grounding electrodes, and can be used for measurements in a small space at the freezing station construction site. It does not require disconnecting the system power supply or disconnecting the grounding electrode and the grounding wire, and is a live operation, which reduces measurement preparation time. There is no need to use a ground resistance megohmmeter, and the three voltages are obtained through a voltmeter, making the measurement operation simpler. This measurement method can also be used to detect ground resistance in other electrical locations outside the freezing station, such as industrial plants, communication stations, etc.

[0044] Furthermore, the measurement of U t 、U t1 When the voltmeter is connected in parallel between the outer shell of the electrical equipment and the ground, measure U t2 When the voltmeter is connected in parallel with the grounding resistor R B between the non-grounded end and the casing of the electrical equipment; the voltmeter used can be a conventional voltmeter, either mechanical or electronic. Note that the voltmeter range must be greater than the secondary phase voltage of the distribution transformer, that is, U0. The specific range of the voltmeter depends on the voltage of the power supply and distribution system on site of the freezing station.

[0045] Furthermore, the short-circuit switch has a delay adjustable function, and the delay time is adjustable within 0-5s; specifically, the delay time of the short-circuit switch in step S3 and step S4 is different: in step S3, when repeated grounding is not performed in the freezing station or repeated grounding is disconnected, the delay time is 0-5s; in step S4, when repeated grounding is performed in the freezing station, the delay is 0-1s, and the basis for the delay setting is Article 411.3.2.3 and Article 411.3.2.4 of "GB16895.21-2011 / IEC60364-4-41:2005"; The protection switch has the functions of adjustable delay and action current, and the delay time is adjustable within 0-5s; specifically, the delay time setting range of the protection switch is consistent with that of the short-circuit switch, and is divided into two cases: the first case is that in step S3, when repeated grounding is not performed in the freezing station or repeated grounding is disconnected, the delay time is set to 0-5s; the second case is that repeated grounding is performed in the freezing station in step S4, the delay time is set to 0-1s; in actual setting, the delay of the protection switch can be 0.1S longer than that of the short-circuit switch; the action current setting range of the protection switch is greater than or equal to 1.3 times the short-circuit current I d , where the optimal value of the protection switch operating current is 1.3 times I d The selection of the optimal operating current is based on the fourth edition of the "Industrial and Civil Power Supply and Distribution Design Manual", Section 11.9.6 "Inter-stage coordination of selective circuit breakers and non-selective circuit breakers".

[0046] Furthermore, the derivation process of formula (1) includes the following steps:

[0047] Step a) Based on the distribution line model, obtain the impedance value Z of L line, PE line, and PEN lineL , Z PEN , Z PE , as known; then we have

[0048] U t =I d *(Z PE +Z PEN ) (2);

[0049]

[0050] U t2 =I d *Z PE (4);

[0051] in, Since the impedance value Z of L line, PE line and PEN line L , Z PE N, Z PE The sum is in milliohms, and R A 、R B The total is in tens of ohms, so R B After, R B Series R A After that, Z PEN The diversion effect of R is negligible, that is, B Before and after, the total circuit current is still in accordance with I d Calculate, that is, the short-circuit current I d = short-circuit current I d ';

[0052] Step b) Subtract formula (3) from formula (2) and subtract formula (4) from formula (2) to obtain:

[0053]

[0054] U t -U t2 =I d *Z PEN (6);

[0055] Step c) Divide both sides of the equal signs of formula (5) and formula (6) to obtain:

[0056]

[0057] After further sorting, we get

[0058]

[0059] Therefore, U is measured by the method of the present invention. t 、U t1 、U t2The grounding resistance R can be directly calculated B , and can be used directly to determine whether the grounding resistance meets the specification requirements, where the measured U t 、U t1 、U t2 The maximum value of will not exceed U0; In addition, U0 and Z appearing in the above formula L , Z PE , Z PEN The impedance values of L line, PE line and PEN line are Z, which are only involved in the derivation of formula (1) and do not need to be measured. L , Z PEN , Z PE The sum is in milliohms, and R A ,R B The total is in tens of ohms, so R B After, R B Series R A After that, the shunt effect of ZPEN is ignored, resulting in a small error, but the shunt error is less than 0.1%. Considering that the voltage drop error becomes 10 times larger when multiplied by the resistance value, the error of the final calculated result is also less than 1%; therefore, the derivation process of formula (1) used in the measurement method of the present invention is logically rigorous, the result is accurate, and meets the requirements of actual measurement.

[0060] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the claims of this patent application.

Claims

1. A method for measuring the grounding resistance value in a temporary power system in a freezing station, characterized in that: The following steps are involved: S1 specifies the grounding resistance R of the transformer (1) in the preceding substation supplying power to the freezing station. A , as known; S2 is equipped with a short-circuit switch at the point where the L line enters the outer shell of the electrical equipment. The short-circuit switch has a function of automatically tripping after a delay after closing. The electrical equipment is located at the rear stage of the freezing station distribution box (2); S3 is in the freezing station. Without repeated grounding or disconnecting repeated grounding, close the short-circuit switch, short-circuit the L line with the outer shell of the electrical equipment, and measure the voltage U between the outer shell of the electrical equipment and the earth. t , the short-circuit switch automatically trips after a delay; S4 is in the freezing station and is repeatedly grounded. The grounding resistance is R B ; Close the short-circuit switch, short-circuit the L line with the outer shell of the electrical equipment, and measure the voltage U between the outer shell of the electrical equipment and the earth. t1 , the voltage U of the electrical equipment shell to the equipotential connection t2 ; S5 is based on the known grounding resistance R A and the measured U t 、U t1 、U t2 Calculate the grounding resistance R according to the following formula B , 2. The method for measuring the grounding resistance value in the temporary power system in the freezing station according to claim 1 is characterized in that: Before step S2, the method further includes step S0: setting a protection switch at the freezing station distribution box (2).

3. The method for measuring the grounding resistance value in the temporary power system in the freezing station according to claim 1, characterized in that: The short-circuit switch has a delay adjustable function, and the delay time is adjustable within 0-5s.

4. The method for measuring the grounding resistance value in the temporary power system in the freezing station according to claim 2, characterized in that: The protection switch has the functions of time delay and action current adjustment, and the time delay is adjustable within 0-5s.

5. The method for measuring the grounding resistance value in the temporary power system in the freezing station according to claim 1, characterized in that: The short-circuit current generated by the short circuit in step S4 is I d The short-circuit current generated by the short circuit in step S5 is I d ', then I d =I d '.

6. The method for measuring the grounding resistance value in the temporary power system in the freezing station according to claim 5, characterized in that: The acquisition of formula (1) includes the following steps: Step a) Based on the model of the distribution line, obtain the impedance value Z of the L line, PE line, and PEN line L , Z PEN , Z PE , as known; then we have Ut=Id*(ZPE+ZPEN) (2); Ut2=Id*ZPE (4); Step b) Subtract formula (3) from formula (2) and subtract formula (4) from formula (2) to obtain: Ut-Ut2=Id*ZPEN (6); Step c) Divide equation (5) and equation (6) to obtain: After further arrangement, we get formula (1).

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