Emergency guarantee power supply circuit for key load of direct current system
By introducing small-capacity emergency battery packs, undervoltage relays, and timers into the DC system of the substation, an isolated switching and self-testing circuit is formed, which solves the problem of protection devices failing to operate due to insufficient implicit capacity. This achieves highly reliable emergency power supply and periodic discharge testing, avoids over-discharge losses, and ensures successful fault clearing.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- STATE GRID SHANDONG ELECTRIC POWER CO JUYE POWER SUPPLY CO
- Filing Date
- 2026-02-12
- Publication Date
- 2026-05-15
AI Technical Summary
In the existing technology, when a primary system fault causes a drop in the station's AC voltage, if the battery bank is unable to maintain the bus voltage within a few seconds due to insufficient implicit capacity, the protection device may fail to operate due to undervoltage or maloperation. The circuit breaker's opening and closing coils may also lack sufficient energy to trip, resulting in failure to clear the fault and an expansion of the accident scope.
A small-capacity emergency battery pack, undervoltage relay, timer, intermediate relay, and discharge resistor are added between the original DC bus and the battery pack to form an isolated switching and daily self-test circuit. This allows the emergency battery to be seamlessly connected to the bus power supply within milliseconds. Periodic discharge tests are achieved through closed-loop control of the timer and undervoltage relay to avoid latent capacity failure and over-discharge losses.
It ensures that the protection device and the circuit breaker opening and closing coils can complete the fault clearing within seconds, avoiding the hidden risk of failure to operate caused by the failure of hidden capacity, realizing maintenance-free, highly reliable and long-life emergency power supply, and eliminating over-discharge loss through regular testing.
Smart Images
Figure CN122052288A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of emergency power supply technology for DC power supplies in substations, specifically to an emergency power supply circuit for critical loads in a DC system. Background Technology
[0002] Substation DC operating power supplies generally adopt a parallel power supply method of "charging module + battery bank": During normal operation, the charging module feeds power to the DC bus through isolation diodes, while simultaneously float-charging the battery; once the AC side loses power or the charging module fails, the battery bank immediately discharges to the bus through the same diode, providing uninterrupted DC power to relay protection, circuit breaker opening and closing coils, and control circuits. Under the above float-charging mechanism, the battery terminal voltage is always clamped near the equalization charge value, and latent defects such as plate breakage, poor terminal connection, and increased internal resistance of individual cells cannot be exposed. Operators can only rely on annual verification discharge tests to judge capacity, which has a long test cycle, high reliance on manual labor, and a monitoring gap between two tests. When a primary system fault causes a drop in the station's AC voltage, if the battery bank cannot maintain the bus voltage within a few seconds due to insufficient latent capacity, the protection device will fail to operate or will malfunction due to undervoltage, and the circuit breaker opening and closing coils will not be able to trip due to insufficient energy, resulting in failure to clear the fault and expansion of the accident scope; there is also the problem that the floating charge state cannot identify capacity failure. Summary of the Invention
[0003] The purpose of this invention is to provide an emergency backup power supply circuit for critical loads in a DC system, in order to solve the problem in the prior art where, when a primary system fault causes a drop in the AC voltage of the station service, if the battery pack is unable to maintain the bus voltage within a few seconds due to insufficient implicit capacity, the protection device will fail to operate or will malfunction due to undervoltage, and the circuit breaker's opening and closing coils will be unable to trip due to insufficient energy, resulting in failure to clear the fault and an expansion of the accident scope.
[0004] To achieve the above objectives, the present invention provides the following technical solution: an emergency backup power supply circuit for critical loads of a DC system, comprising an original DC bus, an original battery pack, a charging module, a first isolation diode, a second isolation diode, a small-capacity emergency battery pack, a DC control switch, an undervoltage relay, a timer, a first intermediate relay, a second intermediate relay, a discharge resistor, and an alarm interface for a monitoring system.
[0005] When the voltage of the original DC bus drops due to AC power failure and insufficient capacity of the original battery pack, the small-capacity emergency battery pack instantly supplies power to the original DC bus through the closed normally open main contacts, ensuring uninterrupted operation of critical loads within the few seconds required for automatic transfer switching.
[0006] Furthermore, the positive terminal of the charging module is connected to the original DC bus via a first isolation diode, and the positive terminal of the original battery pack is connected to the original DC bus via a second isolation diode. The cathodes of the two diodes face the original DC bus together to prevent the original DC bus from supplying reverse power to the charging module or the original battery pack.
[0007] Furthermore, the positive terminal of the small-capacity emergency battery pack is connected to the original DC bus via the normally open main contact of the DC control switch and the first intermediate relay, and its negative terminal shares a common ground with the negative terminal of the original DC bus.
[0008] Furthermore, the coil of the undervoltage relay is connected in parallel across the two ends of the small-capacity emergency battery pack, and its normally open contact is connected in series in the power input circuit of the timer, so as to allow the timer to be energized only when the voltage of the small-capacity emergency battery pack is higher than a set threshold.
[0009] Furthermore, the timer is powered by a small-capacity emergency battery pack, and its output contacts are connected in series with the normally open contacts of the undervoltage relay to control the on / off state of the first intermediate relay coil.
[0010] Furthermore, the normally closed auxiliary contact of the first intermediate relay is connected in series with the normally open contact of the undervoltage relay to control the coil of the second intermediate relay. The normally open contact of the second intermediate relay is connected in series with a discharge resistor and then bridging the two ends of the small-capacity emergency battery pack to form a periodic automatic discharge test circuit.
[0011] Furthermore, the normally closed contact of the undervoltage relay is connected to a remote monitoring system to issue a replacement alarm signal when the voltage of the small-capacity emergency battery pack falls below the threshold.
[0012] Furthermore, the timer is a daily cycle type, set to shut down for 3 minutes every day, causing the first intermediate relay coil to lose power, thereby forcing the small-capacity emergency battery pack to disconnect from the original DC bus and automatically enter the discharge test state.
[0013] Furthermore, the operating threshold of the undervoltage relay is set to 85% to 90% of the rated voltage, which is used to issue an alarm and prevent the small-capacity emergency battery pack from being connected to the bus in the early stage of capacity decay.
[0014] The normally open main contact of the first intermediate relay has a rated current ≥10A, ensuring that it can reliably carry the maximum impact current of the circuit breaker tripping coil within 5s.
[0015] A resettable fuse is connected in series in the normally open contact circuit of the second intermediate relay to quickly cut off the circuit when the discharge resistor experiences abnormal overcurrent, thus preventing over-discharge of the small-capacity emergency battery pack.
[0016] Furthermore, the normally closed contact of the undervoltage relay is optically isolated from the input of the remote monitoring system to improve the anti-interference capability when the DC bus negative pole grounding is abnormal.
[0017] Compared with existing technologies, this invention adds an isolated switching and daily self-testing circuit between the original DC bus and the battery bank, consisting of a small-capacity emergency battery bank, an undervoltage relay, a timer, an intermediate relay, and a discharge resistor. This allows the small-capacity battery to seamlessly connect to the bus within milliseconds and provide power for several seconds when the station's AC power fails and the original battery capacity suddenly drops. This ensures that the protection devices, circuit breaker opening and closing coils, and control circuits can complete fault clearing and automatic switching actions. At the same time, the closed-loop control of the timer and undervoltage relay automatically disconnects from the bus and performs a quantitative discharge test every day. If the voltage is not up to standard, the connection is locked and an alarm is uploaded. This eliminates the hidden risk of failure to operate caused by latent capacity failure and avoids over-discharge losses, achieving maintenance-free, highly reliable, and long-life emergency protection. Attached Figure Description
[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.
[0019] Figure 1 A schematic diagram of the circuit principle provided for an embodiment of the present invention;
[0020] Figure 2 This is a schematic diagram of the signal circuit principle of the device provided in an embodiment of the present invention. Detailed Implementation
[0021] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.
[0022] As attached Figure 1 As shown,
[0023] Example 1: This invention provides an emergency backup power supply circuit for critical loads in a DC system, comprising: a primary DC bus, a primary battery pack, a charging module, a first isolation diode, a second isolation diode, a small-capacity emergency battery pack, a DC control switch, an undervoltage relay, a timer, a first intermediate relay, a second intermediate relay, a discharge resistor, and an alarm interface for a monitoring system.
[0024] When the voltage of the original DC bus drops due to AC power failure and insufficient capacity of the original battery pack, the small-capacity emergency battery pack instantly supplies power to the original DC bus through the closed normally open main contacts, ensuring uninterrupted operation of critical loads within the few seconds required for automatic transfer switching.
[0025] The positive terminal of the charging module is connected to the original DC bus via the first isolation diode, and the positive terminal of the original battery pack is connected to the original DC bus via the second isolation diode. The cathodes of the two diodes face the original DC bus to prevent the original DC bus from supplying reverse power to the charging module or the original battery pack. The small-capacity emergency battery pack consists of 18 12V / 4Ah batteries connected in series, with a rated output voltage of 216V, which matches the nominal voltage of 220V of the original DC bus.
[0026] In addition, the positive terminal of the small-capacity emergency battery pack is connected to the original DC bus via the normally open main contact of the DC control switch and the first intermediate relay, and its negative terminal shares the same ground as the negative terminal of the original DC bus.
[0027] It should be noted that the coil of the undervoltage relay is connected in parallel across the two ends of the small-capacity emergency battery pack, and its normally open contact is connected in series in the power input circuit of the timer, so that the timer is allowed to be energized only when the voltage of the small-capacity emergency battery pack is higher than the set threshold.
[0028] Furthermore, the timer is powered by a small-capacity emergency battery pack, whose output contacts are connected in series with the normally open contacts of the undervoltage relay to control the on / off state of the first intermediate relay coil.
[0029] Furthermore, the normally closed auxiliary contact of the first intermediate relay is connected in series with the normally open contact of the undervoltage relay to control the coil of the second intermediate relay. The normally open contact of the second intermediate relay is connected in series with a discharge resistor and then bridging the two ends of the small-capacity emergency battery pack to form a periodic automatic discharge test circuit. The discharge resistor is a 50Ω, 50W power resistor, and its discharge current value takes into account both the test effectiveness and the capacity protection of the small-capacity emergency battery pack.
[0030] Furthermore, the normally closed contact of the undervoltage relay is connected to a remote monitoring system to issue a replacement alarm signal when the voltage of a small-capacity emergency battery pack falls below a threshold.
[0031] The timer is a daily cycle type, set to shut off for 3 minutes every day, causing the first intermediate relay coil to lose power, thereby forcing the small-capacity emergency battery pack to disconnect from the original DC bus and automatically enter the discharge test state.
[0032] In addition, the operating threshold of the undervoltage relay is set to 85% to 90% of the rated voltage. This is used to issue an alarm and prevent the small-capacity emergency battery pack from being connected to the bus in the early stage of capacity decay.
[0033] The normally open main contact of the first intermediate relay has a rated current of ≥10A, ensuring that it can reliably carry the maximum impact current of the circuit breaker tripping coil within 5s.
[0034] A resettable fuse is connected in series in the normally open contact circuit of the second intermediate relay to quickly cut off the circuit when the discharge resistor experiences abnormal overcurrent, thus preventing over-discharge of the small-capacity emergency battery pack.
[0035] Furthermore, the normally closed contacts of the undervoltage relay are optically isolated from the inputs of the remote monitoring system, improving the anti-interference capability when the negative ground of the DC bus is abnormal; all relays, timers, resistors and diodes are integrated into a 2U standard chassis, which can be inserted into the spare slot of the DC panel in the substation, realizing uninterrupted power supply modification and portable emergency mobile use.
[0036] When using this invention, follow these steps:
[0037] Step a: Push the entire chassis into the spare rail of the DC power supply, and connect the original DC bus positive and negative terminals, the original battery pack positive terminal, and the charging module output positive terminal to the chassis bus positive, bus negative, battery positive, and charging positive terminals respectively, to complete the parallel connection of the main circuit and the isolation diode.
[0038] Step b: Connect the positive and negative terminals of the small-capacity emergency battery pack to the front end of the main contact of the first intermediate relay via the DC control switch inside the chassis, and then connect the rear end of the main contact of the relay to the positive terminal of the bus to form a parallel branch that can be switched on or off at any time.
[0039] Step c: Use the coil of the undervoltage relay to directly monitor the voltage of the small-capacity emergency battery pack, and connect its normally open contact in series with the timer power supply circuit so that the timer can only be powered on and start timing when the battery voltage is qualified.
[0040] Step d: Connect the output contact of the timer in series with the normally open contact of the undervoltage relay to control the coil of the first intermediate relay, so as to achieve a power failure reset once a day; at the same time, drive the coil of the second intermediate relay in the series circuit of the normally closed auxiliary contact of the first intermediate relay and the normally open contact of the undervoltage relay, so that the normally open contact of the second intermediate relay controls the discharge resistor to be connected across the two ends of the small-capacity emergency battery pack, and complete the automatic discharge test.
[0041] Step e: Connect the normally closed contact of the undervoltage relay to the remote monitoring input, and send an alarm signal when the battery voltage is lower than the threshold.
[0042] Step f: When the AC system is normal, the charging module supplies power to the bus via the first isolation diode, the small-capacity emergency battery pack is float-charged via the same bus, the first intermediate relay remains energized, its main contacts are closed, the battery is online but does not carry current.
[0043] Step g: After the timer enters the daily setting window, its output contact opens, the first intermediate relay coil is de-energized, the main contact opens to disconnect the small-capacity emergency battery pack from the bus, and the normally closed auxiliary contact closes, the second intermediate relay is energized, the discharge resistor is engaged, and capacity verification is performed. If the voltage is consistently higher than the threshold, the first intermediate relay re-energizes after the timer window ends, and the battery returns to the online state. If the voltage is lower than the threshold, the normally open contact of the undervoltage relay opens, the timer cannot be energized again, the battery remains isolated, and an alarm is uploaded.
[0044] Step h: When AC power fails and the original battery pack cannot maintain the bus voltage, the bus voltage is lower than the voltage of the small-capacity emergency battery pack. The closed main contacts of the first intermediate relay immediately send battery energy to the bus to provide continuous power supply for the protection and operation circuit for a few seconds. After AC power is restored, the bus voltage rises, the first isolation diode is turned on again, and the small-capacity emergency battery pack automatically disconnects from the power supply and resumes float charging.
[0045] Step i: After receiving the alarm, the operator can replace the entire small-capacity emergency battery pack simply by disconnecting the DC control switch. During the entire process, the original DC bus remains energized, and no protection or control equipment needs to be shut down.
[0046] Example 2 is basically the same as the previous example, except that it is used differently.
[0047] S1. Device installation
[0048] S1.1 Slide the chassis into the standby 2U position of the DC panel in the substation. The chassis is pre-installed with the first isolation diode D1, the second isolation diode D2, the first intermediate relay KM1, the second intermediate relay KM2, the undervoltage relay KV, the timer KT, the discharge resistor R, the resettable fuse F, and the DC control switch QF3.
[0049] S1.2 External Wiring: The original DC bus positive and negative terminals are connected to BUS+ and BUS- respectively; the positive terminal of the original battery pack is connected to BUS+ via the second isolation diode D2; the output of the charging module is connected to BUS+ via QF2 and the first isolation diode D1; the positive terminal of the small-capacity emergency battery pack is connected to BUS+ via the DC control switch QF3 and the main contact of the first intermediate relay KM1, and the negative terminal is connected to BUS-; the undervoltage relay KV coil is connected to the small-capacity emergency battery pack; the power supply of the timer KT is taken from the small-capacity emergency battery pack via the normally open contact of the undervoltage relay KV; the coil of the first intermediate relay KM1 returns to the negative terminal via the timer KT and the normally open contact of the undervoltage relay KV; the coil of the second intermediate relay KM2 is controlled by the normally open contact of the undervoltage relay KV and the normally closed contact of the first intermediate relay KM1 in series, and the normally open contact of the second intermediate relay KM2 is connected across the small-capacity emergency battery pack via the resettable fuse F and the discharge resistor R; the normally closed contact of the undervoltage relay KV is sent to the monitoring via the optocoupler.
[0050] S2, parameter settings: undervoltage relay KV operates at 198V with a hysteresis of 6V; timer KT loses power for 3 minutes daily at 03:00; discharge resistor R = 50Ω.
[0051] S3. Under normal operation, the 220V DC bus is powered by the first isolation diode D1. The small-capacity emergency battery pack is float-charged through the first isolation diode D1. The undervoltage relay KV is energized, the timer KT is energized, the first intermediate relay KM1 is energized, and the second intermediate relay KM2 is de-energized.
[0052] S4. Daily self-test: When timer KT enters the daily power failure window, its output contact opens, the coil of the first intermediate relay KM1 is de-energized, the main contact opens, and the small-capacity emergency battery pack is disconnected from the DC bus. At the same time, the normally closed contact of the first intermediate relay KM1 resets, the coil of the second intermediate relay KM2 is energized, its normally open contact closes, the discharge resistor R is engaged, and a discharge test is performed on the small-capacity emergency battery pack. If the battery voltage remains not lower than 198V during the discharge, timer KT is re-energized after the power failure window ends, the first intermediate relay KM1 is energized again, and the self-test passes. If the battery voltage drops below 198V, the normally open contact of the undervoltage relay KV opens, timer KT cannot be energized again, the first intermediate relay KM1 remains in the released state, the small-capacity emergency battery pack remains isolated, and the normally closed contact of the undervoltage relay KV closes, sending an undervoltage alarm to the monitoring system.
[0053] S5. Fault Activation: When the station's AC power fails and the original battery pack cannot maintain the DC bus voltage, the bus voltage drops. The main contacts of the first intermediate relay KM1, which is already in the closed state, immediately send energy from the small-capacity emergency battery pack to the DC bus, maintaining the bus voltage above 198V for more than 5 seconds, meeting the operational requirements of the protection device and the circuit breaker's opening and closing coils. After AC power is restored, the charging module output rises, the first isolation diode D1 is re-conducted, and the DC bus voltage is higher than the voltage of the small-capacity emergency battery pack. Its main contacts remain in the closed state, but the current is automatically transferred to the charging module, and the small-capacity emergency battery pack resumes floating charging.
[0054] S6. Replacement and maintenance: Open DC control switch QF3, remove the whole unit, replace the battery, close DC control switch QF3, reset the alarm, and ensure uninterrupted power supply to the DC bus throughout the process.
[0055] Example 3 is basically the same as the previous example, except that it also includes the following: Figure 2 The device signal circuit shown;
[0056] In the undervoltage alarm signal circuit, a set of normally closed contacts of the undervoltage relay (KV) is used to drive the alarm signal. When the voltage of the small-capacity emergency battery pack falls below a set threshold (such as 90% of the rated voltage, i.e., 198V), the coil of the undervoltage relay (KV) is de-energized and reset, and its normally closed contacts close. This closing signal can directly illuminate the "undervoltage alarm" indicator light on the local device, and also be sent to the input interface of the remote monitoring system through an optocoupler isolator to generate a remote alarm signal indicating "emergency battery pack undervoltage" or "needs replacement."
[0057] In the device operation status signal circuit, a set of normally open auxiliary contacts of the first intermediate relay (KM1) is used to indicate the normal operation status of the device. When the coil of the first intermediate relay (KM1) is energized and engaged (i.e., the small-capacity emergency battery pack is in online standby mode), its normally open auxiliary contacts close, driving the local "device operation" indicator light to remain on, indicating that the emergency backup circuit is in normal standby mode;
[0058] In the discharge test status signal circuit, a set of normally open auxiliary contacts of the second intermediate relay (KM2) is used to indicate the discharge test status. When the device enters the daily timed self-test and the second intermediate relay (KM2) is energized to engage the discharge resistor, its normally open auxiliary contacts close, illuminating the local "discharge test" indicator light, clearly indicating that the device is in the automatic capacity test process;
[0059] The integrated fault signal circuit utilizes a set of normally closed auxiliary contacts of the first intermediate relay (KM1) connected in series with the normally open contact of the undervoltage relay (KV) to form a logical AND loop. When the small-capacity emergency battery pack is locked due to low voltage (KV normally open contact opens) and has been forcibly disconnected from the bus (KM1 loses power, normally closed contact closes), this circuit is activated, driving the local "device fault" indicator light. It can also selectively upload the signal to the monitoring system through another isolated channel, indicating that the battery has failed and the device is unusable.
[0060] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.
Claims
1. An emergency backup power supply circuit for critical loads in a DC system, characterized in that, Includes the original DC bus, original battery pack, charging module, first isolation diode, second isolation diode, small capacity emergency battery pack, DC control switch, undervoltage relay, timer, first intermediate relay, second intermediate relay, discharge resistor and monitoring system alarm interface; When the voltage of the original DC bus drops due to AC power failure and insufficient capacity of the original battery pack, the small-capacity emergency battery pack instantly supplies power to the original DC bus through the closed normally open main contacts, ensuring uninterrupted operation of critical loads within the few seconds required for automatic transfer switching.
2. The emergency backup power supply circuit for a critical load in a DC system according to claim 1, characterized in that, The positive terminal of the charging module is connected to the original DC bus via a first isolation diode, and the positive terminal of the original battery pack is connected to the original DC bus via a second isolation diode. The cathodes of the two diodes face the original DC bus together to prevent the original DC bus from supplying reverse power to the charging module or the original battery pack.
3. The emergency backup power supply circuit for a critical load in a DC system according to claim 2, characterized in that, The positive terminal of the small-capacity emergency battery pack is connected to the original DC bus via a DC control switch and the normally open main contact of the first intermediate relay, while its negative terminal shares a common ground with the negative terminal of the original DC bus.
4. The emergency backup power supply circuit for a critical load in a DC system according to claim 3, characterized in that, The coil of the undervoltage relay is connected in parallel across the two ends of the small-capacity emergency battery pack, and its normally open contact is connected in series in the power input circuit of the timer, so that the timer is allowed to be energized only when the voltage of the small-capacity emergency battery pack is higher than a set threshold.
5. The emergency backup power supply circuit for a critical load in a DC system according to claim 4, characterized in that, The timer is powered by a small-capacity emergency battery pack, and its output contacts are connected in series with the normally open contacts of the undervoltage relay to control the on / off state of the first intermediate relay coil.
6. The emergency backup power supply circuit for a critical load in a DC system according to claim 5, characterized in that, The normally closed auxiliary contact of the first intermediate relay is connected in series with the normally open contact of the undervoltage relay to control the coil of the second intermediate relay. The normally open contact of the second intermediate relay is connected in series with a discharge resistor and then connected across the two ends of the small-capacity emergency battery pack to form a periodic automatic discharge test circuit.
7. The emergency backup power supply circuit for a critical load in a DC system according to claim 6, characterized in that, The normally closed contact of the undervoltage relay is connected to a remote monitoring system to issue a replacement alarm signal when the voltage of a small-capacity emergency battery pack falls below a threshold.
8. The emergency backup power supply circuit for a critical load in a DC system according to claim 7, characterized in that, The timer is a daily cycle type, set to turn off for 3 minutes every day, causing the first intermediate relay coil to lose power, thereby forcing the small-capacity emergency battery pack to disconnect from the original DC bus and automatically enter the discharge test state.
9. An emergency backup power supply circuit for a critical load in a DC system according to claim 8, characterized in that, The operating threshold of the undervoltage relay is set to 85% to 90% of the rated voltage. This is used to issue an alarm and prevent the small-capacity emergency battery pack from being connected to the busbar in the early stage of capacity decay. The normally open main contact of the first intermediate relay has a rated current ≥10A, ensuring that it can reliably carry the maximum impact current of the circuit breaker tripping coil within 5s. A resettable fuse is connected in series in the normally open contact circuit of the second intermediate relay to quickly cut off the circuit when the discharge resistor experiences abnormal overcurrent, thus preventing over-discharge of the small-capacity emergency battery pack.
10. An emergency backup power supply circuit for a critical load in a DC system according to claim 9, characterized in that, The normally closed contact of the undervoltage relay is optically isolated from the input of the remote monitoring system, which improves the anti-interference capability when the DC bus negative pole grounding is abnormal.