CN214755490U

CN214755490U - Neutral point protection device for non-effective grounding diesel generator set

Info

Publication number: CN214755490U
Application number: CN202023136649.6U
Authority: CN
Inventors: 张守和; 平原; 赵国军; 周金木
Original assignee: Cggc Un Power Co ltd
Current assignee: Cggc Un Power Co ltd
Priority date: 2020-12-23
Filing date: 2020-12-23
Publication date: 2021-11-16
Anticipated expiration: 2030-12-23

Abstract

The utility model discloses a non-effective ground connection diesel generating set neutral point protection device, include: the system comprises a neutral point grounding resistor, a sensing resistor, a zero sequence current sensor, a multifunctional monitoring relay, an intermediate relay and a terminal transfer box; the device comprises a medium-voltage single-core cable, a low-voltage single-core cable, two cores of a control cable, multiple cores of the control cable, a single core of the control cable, a working power line and a grounding line of the device; the utility model has the advantages that: the ground fault of the diesel generating set is protected by controlling a set breaker and a set controller; the neutral point of the generator adopts a high-resistance low-current design, and is applied by combining a high-end precision sensing control technology, so that the damage of fault point current to equipment is greatly reduced while the sensitivity of ground protection is ensured; the structure is simple and compact, and the modularized unit complete scheme is adopted and is independently matched with a diesel generator set; the protection reliability, the flexible expansion of the system and the maintainability are obviously improved.

Description

Neutral point protection device for non-effective grounding diesel generator set

Technical Field

The utility model belongs to the technical field of the unit protection technique and specifically relates to a diesel generating set ground fault neutral point protection control technique, belongs to the electrical fault protection technique.

Background

The requirements of a new generation of data center on the safety and reliability of a power supply system are increasingly improved, and for a core equipment diesel generator set which is used for carrying out an emergency guarantee function, not only are internal fault protection and system fault protection required for the generator set and accurate and reliable matching of the internal fault protection and the system fault protection required, but also the damage degree of fault ignition arc to equipment is reduced as far as possible, so that the protection technology level can synchronously follow the development requirements of the data center. Among various fault types of the power system, the probability of system single-phase short circuit/ground fault is the highest, and particularly, the generator single-phase short circuit/ground fault directly influences the operation of a power station.

To reduce costs, medium voltage generators are not usually designed to withstand full single phase fault current, and therefore the generator neutral needs to be grounded via a resistor. The neutral point resistor generally has two basic configuration modes, one is low-resistance protection, in order to improve fault detection and protection sensitivity, the neutral point resistor generally has a small resistance value, and the configuration has a low risk on the insulation of a generator winding and is also beneficial to fault maintenance safety, however, the fault point current is very large, so that equipment is seriously damaged and high maintenance cost is easily caused, medium-voltage units mostly run in parallel, and the condition is more serious; in addition, when a fault occurs in the generator, even if the breaker is opened, if the engine is cooled and stopped, the fault current still burns the winding, and if the engine is suddenly stopped, the service life of the unit is influenced. The other one is high-resistance protection, which can reduce the current and the destructive power of a fault point, but the fault detection and the protection sensitivity are difficult to realize, and the requirement on the insulation level of the generator is also high.

On the neutral point protection structure, the parallel operation power station has the following types:

(1) the neutral point of each generator is grounded through a contactor and a resistor, and only one neutral point resistor of the running unit is controlled to be put into operation through the contactor. The disadvantage of this solution is that multiple contactor breakpoints and complex logic control are required; once the grounded neutral point resistor is disconnected or during the switching-off period of the unit, the whole system is in an unsafe state of non-grounding, and the reliability of the system is poor;

(2) the neutral point of each generator is fixedly grounded through a resistor. The scheme has the defects that the current of a ground fault point of the parallel operation system is large, and the damage is serious when the internal winding of the generator fails;

(3) the generator neutrals are connected together and grounded via a common resistor and/or contactor. The disadvantage of this scheme is that the third harmonic circulating current is large; the system has poor operation safety and flexibility; the voltage of the neutral point of each unit is increased due to the earth fault of any point of the system, and the safety of maintenance is threatened; the opening of the contactor causes an unsafe state of non-grounding of the system;

(4) high-low resistance hybrid neutral control system. The scheme adopts low-resistance protection for external ground faults, adopts high-resistance protection for internal faults of the generator and utilizes differential protection cooperation, and although the defects of the schemes are overcome, the system is complex and the equipment investment is large.

The protection coordination of the ground fault in different areas is less considered in various application schemes, when the ground fault occurs in a load wiring system, the power supply side protection can trip out in a grade-by-grade mode, the protection loses selectivity, the fault range is enlarged, and the system protection coordination is complex and difficult.

According to the new development requirement of high-end users on a security power supply system, protection technology upgrading needs to be carried out aiming at the ground fault of the generator, the defects in the prior art are overcome, and a simple, reliable and easily-expanded neutral point protection system matched with the unitized unit is constructed by combining lower cost and modular design with the existing equipment.

Disclosure of Invention

In order to solve the problems, the utility model designs a neutral point protection device of a non-effective grounding diesel generator set, which obviously improves the reliability, flexible expansion and maintainability of the system; the damage of fault point current to equipment is greatly reduced while the sensitivity of the ground protection is ensured; the selectivity and the rapidity of the ground fault protection are ensured, and the difficulty and the complexity of fixed value matching are overcome.

The technical scheme of the utility model is that:

non-effective ground connection diesel generating set neutral point protection device includes: the system comprises a neutral point grounding resistor NER, a sensing resistor SR, a zero sequence current sensor ZSCS, a multifunctional monitoring relay MMR, an intermediate relay K and a terminal transfer box JB; the cable comprises medium-voltage single-core cables H1 and H2, low-voltage single-core cables L1 and L2, two cores C1, C2 and C4 of a control cable, multiple cores C3, C5 and C6 of the control cable, a single-core C7 of the control cable, a device working power supply line and a device working ground line.

The utility model discloses protection system protects diesel generating set DG's ground fault through control unit circuit breaker GCB and unit controller AC.

The specific connection relationship is as follows:

a neutral point resistor NER grounding end E is connected with a grounding system through a cable L2, and a neutral point resistor NER high-voltage end F is connected with a sensing resistor SR high-voltage end N through a cable H2; a cable H2 penetrates through a primary core hole of the ZSCS; a main grounding terminal G of the sensing resistor SR is connected with a grounding system through a cable L1 and a sampling grounding terminal G1, and then through a cable C7, and a high-voltage terminal N of the sensing resistor SR is connected with a neutral point NN of the generator through a cable H1; the sampling end R of the sensing resistor SR and the grounding point of the system are connected to a terminal junction box JB through a cable C1, the SEC winding X1/X2 end of the zero-sequence current sensor ZSCS is connected to the terminal junction box JB through a cable C2, the terminal junction box JB is connected to No. 45, No. 46, No. 47 and No. 48 ends of the multifunctional monitoring relay MMR through a cable C3, wherein the sampling end R corresponds to the No. 45 end, the grounding corresponds to the No. 46 end, the SEC winding X1 end corresponds to the No. 47 end, and the X2 end corresponds to the No. 48 end; the main output normally-open 17/18 end of the multifunctional monitoring relay MMR controls the brake-separating loop of the generator circuit breaker GCB through a cable C4; the MMR auxiliary output normally-open point 42/43 controls the coil of the intermediate relay K, the normally-closed point of the relay K provides a ground fault action signal for the controller AC through a first group of double cores of a cable C6, and the controller AC outputs a tripping inhibiting signal to inhibit the MMR tripping output function when only the NER fault exists and the system does not have the ground fault through the 25/26 input end of a second group of double core control monitoring relay MMR of a cable C6.

The intermediate relay K normally-on point, the MMR auxiliary output normally-on point 39/40 end of the multifunctional monitoring relay, and the MMR input point 19/20 end are connected to a control room through a cable C5 for monitoring by a user.

The multifunctional monitoring relay MMR working power supply and the intermediate relay K loop working power supply use a DC110V direct current system, and the G end of the relay MMR is connected with a grounding system.

The connecting structure forms a whole set of neutral point grounding protection unit which is independently matched with a diesel generating set DG; and a plurality of diesel generator sets which are matched with each other are connected with the MV medium-voltage parallel operation bus through respective circuit breakers GCB.

The function of the above connection scheme is explained as follows:

1. the neutral point resistor NER provides a zero-sequence current channel of the ground fault and limits the fault current, and the damage of the fault point current to equipment is reduced by adopting a higher resistance value;

2. the zero-sequence current sensor ZSCS detects the neutral point loop current and inputs a current signal into the multifunctional monitoring relay MMR through a terminal transfer box JB, and the zero-sequence current sensor ZSCS is an i-Gard device and is characterized by a high-precision large-range large-transformation-ratio current sensing mode;

3. the sensing resistor SR monitors the NER neutral point loop disconnection or resistance value abnormity through neutral point voltage sampling, a sampling signal is input into the multifunctional monitoring relay MMR through the terminal junction box JB, the sensing resistor SR is an i-Gard device, and the high-voltage input equivalent impedance is far larger than the high-resistance NER, so that the high-reliability sealing and curing structure is high in reliability, and the weak shunt of the neutral point loop is ignored. The matching combination of SR and ZSCS makes the high sensitivity of the large-resistance NER ground protection possible;

4. the MMR of the multifunctional monitoring relay comprehensively processes the sampling signals according to the current and the voltage of the neutral point, judges and identifies the state of the system, and monitors and protects two conditions of the system ground fault and the NER loop fault: (1) when the system has a ground fault, an output end of a normally open point 42/43 sends a ground fault alarm signal, the ground fault alarm signal is output through an intermediate relay K in an expanded mode, meanwhile, MMR tripping inhibition is relieved through a controller AC, and an output end of a normally open point 17/18 of the MMR relay controls a generator set GCB to be switched off and isolated from the fault; the controller AC triggers the unit to enter a shutdown program, and can be set as cooling shutdown, adjustable delay shutdown or instant emergency shutdown as required, and because the NER adopts a large-resistance design, the current of a fault point is small, and the damage to the generator is small, the shutdown mode can be set as cooling shutdown to maintain the service life of engine parts; (2) when the NER fault or the neutral point loop is abnormal, an NER fault alarm signal is sent out by an 39/40 normally open point output end, if the system does not have a ground fault at the moment, the MMR auxiliary output 42/43 and the intermediate relay K do not act, the controller AC returns a passive contact closing signal to the MMR input point 25/26 according to the normally closed point state of the relay K to serve as a tripping inhibition signal, so that the MMR main output does not act, the tripping of a unit is avoided, and only NER fault or abnormality is prompted to an operator; if the generator set is tripped out of operation when the NER fails, only the corresponding setting of the controller AC needs to be modified. If the MMR is not subjected to trip suppression through the controller AC, the normally closed point of the relay K can be directly connected with the input end of the MMR relay 25/26 to be used as a trip suppression alternative;

5. and coordination of hierarchical protection of system areas. The selective protection of the system earth fault range is difficult to match only by a fixed value, and the adoption of a zone level matching control mode is simpler and more reliable. The earth fault of each line of the wiring system is brought into centralized monitoring, an earth fault common alarm signal is output, when any line is distributed with earth fault, the earth fault common alarm signal is input to the MMR relay through the No. 19/20 terminal, at the moment, if the MMR also detects the earth fault, the MMR automatically delays for 0.75 second, thereby avoiding the earth protection override trip of the generator set, and accurately and reliably realizing the selectivity of the protection.

The utility model discloses the setting method as follows:

1. provided is a method for setting ground fault protection. In order to realize the above functions correctly, system setting needs to be performed according to actual project specifications and equipment parameters. The setting is performed by monitoring the dial switch group of the MMR panel of the relay, and the setting method and the related fixed value are explained as follows. The dial switches are divided into five groups, namely system frequency selection, failure mode selection, NER allowed current value, earth fault current setting value and tripping delay. Each dial switch is provided with an upper position and a lower position which are respectively marked as an upper dial U and a lower dial D, and a dial combination scheme is determined according to the protection setting requirement and by combining with a dial value calculation table of an MMR actual product.

The monitoring relay MMR adopts a non-failure working mode, namely, the main output relay and the auxiliary output relay are both in a normally-open point closed effective mode, and the tripping action output of the relay is not caused even if the direct-current working power supply is in voltage loss. The dial switch 1 is placed in the D position.

The monitoring relay MMR adopts a non-tripping memory mode, namely if the direct current working power supply is subjected to voltage loss after the relay trips and during the period of not resetting, after the direct current working power supply is recovered, the output of the main relay and the auxiliary relay do not memorize the previous tripping state, and the protection can act only when the fault is detected again. The dial switch 2 is placed in the D position.

The generator set and the power supply and distribution are power frequency 50Hz systems. The dial switch 11 is placed in the U position.

The neutral resistance NER allows a selected 404 ohm neutral resistance at 10.5KV rated voltage system with a current value set to 15A, and the zero sequence current sensor T6A assumes a one-time-through single turn loop. The dial switches 12-13-14-15-16 are sequentially set to the D-D-D-U-D position combination.

The ground fault operating current setpoint is set to 20% of the NER let-through current, and when the NER let-through current is 15A, the operating current setpoint is 3A. The dial switches 8-9-10 are sequentially set to D-U-U position combination.

The ground fault trip delay is set to 0.55 seconds. The dial switches 3-4-5-6-7 are sequentially set to D-D-U-D-U position combinations.

2. And (5) specifying the fault fixed value of the NER. According to the NER loop current level, the fault monitoring of the NER by the MMR of the relay is divided into two modes: a resistance value measuring mode and a disconnection monitoring mode. MMR analysis sampling data come from a zero sequence current sensor ZSCS and a sensing resistor SR, and the ground fault protection system is ensured to be reliable, accurate and effective through the integrity monitoring of the NER system. The relevant fixed values are cured in the monitoring relay MMR instead of being set with the panel dial switch.

When the relay MMR detects that the NER loop current is larger than 1% of the allowed current of the NER, the relay MMR enters an NER resistance value measuring mode, at the moment, if the NER resistance value monitored by the relay MMR is higher than 150% of the rated resistance value of the relay MMR or lower than 70% of the rated resistance value of the relay MMR, an NER fault alarm is sent out, and when no trip inhibition exists, the main output relay outputs 3.5-second trip control; if the tripping inhibiting signal exists, only an alarm prompt of NER fault/abnormity is sent out. The engineering significance of the fixed values is that through accurate detection, the conditions of any bad electrical contact, local fault of a resistance piece, foreign matters or dust at equipment or an insulating part and the like of a system loop can be sensitively identified in time and an alarm is sent to prompt operation and maintenance personnel.

When the detection current of the neutral point resistance loop of the input relay MMR is less than 1% of the allowable current of the NER and the measurement precision is difficult to meet, the MMR automatically switches to the NER disconnection monitoring mode, and in the mode, the nature judgment is carried out on whether the NER loop is disconnected and opened or the resistance value exists, and disconnection fault alarm is sent out in a delayed mode to prompt operation and maintenance personnel.

The utility model has the advantages that:

(1) the scheme of the neutral point device is designed into a unitized integral module which is independently matched with a diesel generating set, the units are free of structural cross correlation and interference, and a loop is free of a control breakpoint, so that the reliability, flexible expansion and maintainability of the system are obviously improved;

(2) the neutral point of the generator adopts a high-resistance low-fault current design, and the application of a high-end precision sensing technology is combined, so that the damage of the fault point current to equipment is greatly reduced while the sensitivity of the ground protection is ensured;

(3) monitoring the state of a neutral point resistance loop in real time to ensure that a relay protection system works correctly and reliably when the earth fault occurs;

(4) by adopting a protection coordination control technology of regional grading coordination, the selectivity and the rapidity of ground fault protection are ensured, and the difficulty and the complexity of fixed value coordination are overcome;

(5) the method is characterized in that two types of faults of neutral point resistance and system grounding are designed to alarm respectively and independently, a main output relay is controlled by utilizing a trip suppression function, the control modes of the grounding fault and the neutral point resistance fault are distinguished, and the fault control level is optimized;

(6) the neutral point of the generator adopts a single-path cable connection mode, is connected with the neutral point resistor main equipment through the sensing resistor end in parallel, has a simple wiring structure, and ensures the correct installation and accurate measurement conditions of the zero-sequence current sensor;

(7) the multifunctional monitoring relay has various mode settings and parameter structures, can flexibly adapt to various application scenes and system working conditions, is convenient for modularization and standardization of an integration scheme, and forms a miniaturized simple structure.

The present invention will be further explained with reference to the drawings and examples.

Drawings

Fig. 1 is a schematic structural diagram of a technical solution of an embodiment of the present invention.

Detailed Description

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are presented herein only to illustrate and explain the present invention, and not to limit the present invention.

As shown in fig. 1, the neutral point protection device of the non-effective grounding diesel generator set comprises: the system comprises a neutral point grounding resistor NER, a sensing resistor SR, a zero sequence current sensor ZSCS, a multifunctional monitoring relay MMR, an intermediate relay K and a terminal transfer box JB; the cable comprises medium-voltage single-core cables H1 and H2, low-voltage single-core cables L1 and L2, two cores C1, C2 and C4 of a control cable, multiple cores C3, C5 and C6 of the control cable, a single-core C7 of the control cable, a device working power supply line and a device working ground line. The protection system protects the ground fault of the diesel generator set DG by controlling the generator set circuit breaker GCB and the generator set controller AC. In this embodiment, the specifications of the components and materials are configured as follows: neutral point grounding resistance NER (404 omega, 15A, 10s, insulating 12 KV), sensing resistance SR (i-Gard NGRS-110), zero sequence current sensor ZSCS (i-Gard T6A or T9A- -according to the field cable installation condition, 0.2-1200A, 1000/1), multifunctional monitoring relay MMR (i-Gard C-453EM _ SIGMA, DC 110V), intermediate relay K (MY 2 NJ-D2/DC 110V), terminal junction box JB (terminal 2.5mm2, not less than 4 paths); medium voltage single core cables H1, H2 (1C 35mm2, 8.7/15 KV), low voltage single core cables L1, L2 (1C 25mm2, 0.6/1.0 KV), control cables C1, C2, C4 (2C for 3C 2.5mm 2), control cables C3, C6 (4 cores for 5C 2.5mm 2), control cable C5 (6C for 8C 1.5mm 2), control cable single core C7 (1C 4mm 2) and device working power and ground wires (3C 2.5mm 2). The applied electric primary system is 50Hz, the DG of the diesel generating set is 10.5KV and 2000KW, the stator winding is star-connected and is controlled by a set controller AC, the GCB of the set circuit breaker is 12KV and 630A, and the medium-voltage bus is 10.5KV rated voltage grade.

The utility model discloses protection system protects diesel generating set DG's ground fault through control unit circuit breaker GCB and unit controller AC. The sensing resistor SR, the zero-sequence current sensor ZSCS and the multifunctional monitoring relay MMR are i-Gard products.

The specific connection relationship is as follows:

The intermediate relay K normally-on point (system ground fault alarm output), the MMR auxiliary output normally-on point 39/40 terminal (NER fault alarm output) of the multifunctional monitoring relay, and the MMR input point 19/20 terminal (area-level matching control input) are connected to a control room through a cable C5 for monitoring by a user.

The function of the above connection scheme is explained as follows:

The utility model discloses the setting method as follows:

1. provided is a method for setting ground fault protection. In order to realize the above functions correctly, system setting needs to be performed according to actual project specifications and equipment parameters. The setting is performed by monitoring the dial switch group of the MMR panel of the relay, and the setting method and the related fixed value are explained as follows. The dial switches are divided into five groups, namely system frequency selection, failure mode selection, NER allowed current value, earth fault current setting value and tripping delay. Each dial switch has an upper position and a lower position which are respectively marked as U (upper dial) and D (lower dial), and a dial combination scheme is determined according to the protection setting requirement and by combining with a dial value calculation table of an MMR actual product.

The above disclosure is only for the purpose of illustrating particular embodiments of the present invention and is not intended to limit the invention. The technical solutions described in the embodiments can be modified by those skilled in the art, or some technical features can be replaced by equivalents. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. Non-effective ground connection diesel generating set neutral point protection device, its characterized in that: the system comprises a neutral point grounding resistor NER, a sensing resistor SR, a zero sequence current sensor ZSCS, a multifunctional monitoring relay MMR, an intermediate relay K and a terminal transfer box JB; medium-voltage single-core cables H1 and H2, low-voltage single-core cables L1 and L2, two cores C1, C2 and C4 of a control cable, multiple cores C3, C5 and C6 of the control cable, a single-core C7 of the control cable, a working power line and a grounding line of the device;

2. The non-operatively grounded diesel generator set neutral point protection device of claim 1, wherein: the intermediate relay K normally-on point, the MMR auxiliary output normally-on point 39/40 end of the multifunctional monitoring relay, and the MMR input point 19/20 end are connected to a control room through a cable C5 for monitoring by a user.

3. The non-operatively grounded diesel generator set neutral point protection device of claim 1, wherein: the multifunctional monitoring relay MMR working power supply and the intermediate relay K loop working power supply use a DC110V direct current system, and the G end of the relay MMR is connected with a grounding system.