CN1241057A - Improvements in or relating to parallet-feeder directional overcurrent protection - Google Patents

Abstract

When directional overcurrent protection relays are included at the load end of a set of parallel feeders fed from an AC power source, a minimum fault-current threshold is specified based on the potential of a phase-to-phase fault at the source to cause a relay to operate misleadingly. This threshold is, for plain (transformerless) feeders, approximately 50% and, for transformer feeders, approximately 85% (nominally 86.7%) of rated pre-fault load current. These thresholds can, however, be ignored if the relay outputs are processed in a 2-out-of-3 circuit, so that a relay on one phase will only operate its associated circuit breaker if a relay on another phase has also operated, a condition which has been found not to obtain in the case of a source fault.

Description

Overcurrent protection of parallel feeder directivity and improvement thereof

The present invention relates to a kind of device of avoiding directivity overcurrent protection relay involuntary maneuver, described relay is arranged in the parallel feeder of each phase of heterogeneous especially three-phase (but not absolute) AC electric power systems.

(see figure 1) in the known Over Current Protection System, polyphase source (being generally three-phase) 10 power supply by separately and load bus 12,13 and first feed line 20 and the device of parallel connection second feed line 30 that is connected these buses 30 corresponding heterogeneous load 11 of feeding.These relay groups 21/31,22/32 and 23/33 are connected in the feed line 20/30.Each feed line 20 and 30 has non-directivity overcurrent protection relay 21 and 31 respectively, and in the load side of power source bus 12, non-directivity overcurrent relay 23 and 33 is respectively at the mains side of bus 13 of loading simultaneously respectively for directivity overcurrent relay 21 and 31.Under the situation as the single one group of equipment with two kinds of different qualities (seeing below), the latter's two group relaies can be realized.In the alternative device of another kind (Fig. 2), feed line 20/30 is connected respectively to the secondary coil 24 of transformer 25/35, and primary coil 26/36 is fed from the respective side of non-directional relay group 21/31 respectively.

With reference to figure 3 explanations overcurrent relay pattern in general sense, wherein show the three-phase feed line simplifiedly with the single line form, in this example, described single line comprises three parts, and each part has non-directional relay 40/41/42 and relevant current transformer 50/51/52 and breaker apparatus 60/61/62.The actuating of relay is in the overcurrent setting that reduces from AC power to abort situation F and have the response time that similarly reduces, and in canonical system, this response time from a relay to next relay approximately differs 0.4s.When fault F shown in occurring, only need circuit breaker 62 tripping operations in relevant portion, remaining circuit breaker continues to provide closed path with at the A of transformer station, and B, C keep power supply, and the feed of transformer station shown in can being loads 63.Like this, because the lower fault current level (impedance of feed line bigger) relevant and top said according to the classification between the relay of electric current and response time with this abort situation, only there is relay 42 to respond and move, causes circuit breaker 62 tripping operations fault current.In the same way, if break down in mid portion, fault current can be bigger and be used for actuating relay 41, thereby circuit breaker 61 tripping operations are like that.

Relay can have one of three kinds of response characteristics, i.e. moment (supposing not to be the situation of Fig. 3), during change and regularly.Fig. 4 shows back two specific characters, and the curve of time " t " to electric current " I " drawn.Curve 70 expression chronotropic characters, curve 71 expressions are characteristic regularly.Curve 70 provides according to relay and has been checked through the response time that the fault current level changes, at the low-response of the response ratio high current value of reduced-current value.Concerning curve 71, when fault current surpasses particular value I ₁The time, the response time is constant.

Realize the directivity of relay like this: use reference quantity, be generally system voltage, compare, determine " direction " of electric current by the relative phase between these two amounts with electric current.Relay only just responds when direction is its set response direction.Therefore directional relay has two inputs: voltage and current.Usually reference voltage is called " polarizing voltage ".

With reference to figure 5 (a) and 5 (b), they represent the reduced graph of Fig. 1 and 2 respectively, and three-phase system single line block representation comprises the feed line of two parallel connections and relevant directivity and non-directional relay in this block diagram.If suppose in AC system, not break down and this system with full capacity work, each will be by total rated load electric current I in the feed line 20/30 _L1/2nd.But the design of relay is at the maximum load current I that surpasses under the idle situation of one of them feed line of hypothesis _LThe time have a setting of minimal security overcurrent.Therein under the situation about breaking down on feed line, may surpass the electric current setting of one or more relays, cause that or those relay to register (and " picking up ") fault current level, after time delay, make its relevant circuit breaker trip (promptly " ending to connect ")." ending to connect " if just do not remove fault before the time delay of relay expires, just appears certainly.

In the situation of Fig. 5, suppose that position F shown in the figure is on the feed line to break down.Fault or phase-right-phase, or phase-right-ground.When not having fault, power circuit is from the power supply to the load, so 80,81 pairs of normal duty electric currents that therefore flow through of directional relay are normally insensitive.But when F1 broke down, current direction changed, if fault current I _F1Expression then makes part electric current (I for example _F1/ 2) flow into fault branch, remaining (I through non-directional relay 82 _F1/ 2) flow into fault branch through non-directional relay 83 and directional relay 81.The actual value of fault current depends on abort situation and there is no need between branch road etc. separately in each branch road.In these cases, the electric current in the relay 81 is in the correct direction that makes its action.In fact will provide action, at first be that the fault electric current surpasses its fault current threshold value, and secondly, it sets the duration that the response time is shorter than fault.The transformer feed line principle of device of Fig. 5 (b) similarly.

Fig. 6 (a) and 6 (b) show two kinds of possible relay cooperation figure that are used for various relays shown in Figure 5.Under first kind of situation, relay is a relay when having among Fig. 4 the change of characteristic shown in the curve 70, but has according to fault current I _F2The non-directional relay 84,85 and 86 of response time classification.Relay 83 is identical with 85 current threshold setting; (by the way, these settings are in the nonvolatile memory that is stored in the relay). Relay 83 and 85 is provided with identical this reason just, caused initial problem (this problem utilizes the directivity overcurrent relay to solve), promptly in the failure problems at F1 place, relay 85 moved before relay 83, because relay 82 also moves, and has isolated load effectively. Directional relay 80,81 moves under the reduced-current level (making their relevant circuit breaker trips), and their setting is not subjected to the restriction of load current value usually.The situation of Fig. 6 (b) also is similar, and just all relay characteristics are regularly type.

Just as mentioned briefly above, it is possible being incorporated in the function of relay 81 and 83 in the unit, and this can be relay or the digital relay based on microprocessor with two groups of overflow protecting elements that separate.

People know that user tropism's relay is the effective ways that interrupt isolating all feed line faults with minimum system in each branch road.In addition, also have realized that and the current threshold of directional relay need be arranged on below the normal rating load current, because this helps with mode shown in Figure 3 cooperation (classification) to the different relays that exist in the system.But, even to this day, be arranged on below the load current muchly and simultaneously can keep this problem of reliable in action for this relay, any guidance is not provided as yet.In fact, people even thought and also just do not existed directivity protection load-responsive electric current not on non-direction of action about the employed actual problem that is provided with effectively is set.Other authoritative sources hint is pressed empirical rule, and 50% of load current is proper.

Owing to the fault of particular type on feed line, may occur, be dangerous so for directional relay, used low electric current setting, the present invention inventor just makes the result who draws after the correct evaluation to this.The invention enables be provided with reality reliably current threshold become possibility, also provide a kind of simultaneously and do not observed the device of avoiding the possible malfunction of directional relay under the situation of this threshold value.

According to a first aspect of the invention; be provided with the device of the involuntary maneuver of avoiding one or more directivity overcurrent protection relays; described relay be arranged on polyphase ac electric power system a plurality of parallel feeders each feed line each mutually in; described feed line is fed and is presented load successively from AC power; relay is positioned at the load side of described feed line and the power circuit that described power supply is pointed in response; it is characterized in that, only when another relay in mutually also is in the same action state at least, just come into force at the operate condition of a phase repeat circuit.

AC system is a three-phase system, and for each feed line, described device comprises from what the relay relevant with that feed line output was presented 3 gets 2 determination devices.

Relay when relay can be electrotimer or change.

According to a second aspect of the invention; be included in each directivity overcurrent protection relay in mutually of each feed line of a plurality of parallel feeders of polyphase ac electric power system; feed line is the transformer feed line of feeding from AC power and successively to the load power supply; relay is positioned at separately, and the load side of the described feed line of transformer secondary also responds the power circuit of pointing to described power supply; it is characterized in that the minimum that is provided with of the minimal security operating current level of relay is about 85% of the rated load electric current relevant with described feed line.

Minimal security operating current level be made as the rated load electric current 86% and 87% between, preferably 86.7% of the rated load electric current.

Below with reference to accompanying drawing the present invention is described by way of example, in the accompanying drawings:

Fig. 1 is the schematic diagram of the common parallel feed line apparatus of three-phase, and this device comprises non-directivity and directivity overcurrent relay;

Fig. 2 is the equivalence figure of Fig. 1, just relates to the transformer feed line;

Fig. 3 shows and is used in usually along the classification of feed line between the relay of different piece;

The comparison diagram of relay characteristic and electrotimer characteristic when Fig. 4 is change;

Fig. 5 (a) and 5 (b) have represented the common and transformer parallel feed line apparatus under the feed line fault simplifiedly respectively;

When the typical case that Fig. 6 (a) and 6 (b) show shown in Fig. 5 (a) and 5 (b) device respectively becomes and the timing response classification;

Fig. 7 is the schematic diagram that shows the single three-phase transformer feeder equipment of B-C phase power failure;

Fig. 8 relates to occur before the phase of B-C shown in Fig. 7 power failure and the transformer afterwards and the voltage and current polar plot group of primary coil;

Fig. 9 shows the voltage and current polar plot about the action of relay characteristic and inhibition zone;

Figure 10,11 with 12 with common feed line situation under Fig. 7,8 and 9 corresponding, Figure 12 shows the actuating of relay characteristic of all three phase relaies, and

Figure 13 shows and comprises the 3 common parallel feed devices of three-phase of getting 2 decision-making circuits according to an aspect of the present invention.

Fig. 7 is presented at the malfunction of (seeing Fig. 2 and Fig. 5 (b)) under the transformer feed situation, and the inventor wants to get rid of its threat to the action message of the directional relay of low current setting.Among Fig. 7, only show a pair of three-phase parallel feeder, because it is the general operating characteristics to the significant directional relay of the present invention.Direction overcurrent relay 22 shown in being fed to from the secondary coil 24 of the Y-connection of Dyn11 transformer.

In this case, not appearing at position F1 among Fig. 5 in fault, is power supply 10 itself between phase B and the C but appear at two-phase.Fig. 8 show before the fault and fault after in transformer (high pressure [HV] circuit) and secondary coil (low pressure [LV] circuit) mobile different electric currents.As seen, the LV load current level between age at failure on the two-phase is 86.7% of the preceding level of fault, and it is zero substantially that residue goes up mutually.

The curve of Fig. 9 is an operating characteristics of checking two specific LV directivity elements of big electric current between the HV age at failure.As can be seen, C phase directivity checking elements the relation between polarizing voltage and the operating current, this relation may cause unexpected protection action.If the setting of LV directivity protective current is lower than 86.7% of fault preload electric current, this involuntary maneuver just may.

For parallel transformer feed line, the design criterion of standard is to use one of them carrying maximum system load when a feed line is out of service.Under the situation of two parallel feeders, under to the situation of some short-term overload capacity without any allowance, the maximum fault preload electric current of each feed line is 50% of a rated current.All obtain using if use this criterion and two feed lines, the directional relay of the bus end of then loading just can be set to be low to moderate 43.3% of rated current safely, so that provide safeguard protection between the HV age at failure.

When not using one of them parallel feeder intentionally for maintenance purpose, the load current before the fault that transformer LV directional relay is checked will be greatly to 100% of rated current.Prevent HV phase-in order to provide to the maximum security of a phase fault; the setting of directivity protection should not be lower than 86.7% of rated current; but be provided with to such an extent that low a little again (for example: about 85%, more precisely between 86% and 87%) reduces the fail safe on border.When two parallel feeders are only arranged, certainly, when not working, a feed line do not need user tropism's protection.When being provided with three three-phase feed lines, using the fault preload electric current under whole feed line situations to be 66.7% of rated current, so LV directivity protection should not be set to be lower than the 57.7% reliable to guarantee the directivity protection of rated current.

Situation is similar shown in Figure 10 to 12 and Fig. 7 to 9, but that relate to is common parallel feeder (among Fig. 1 and Fig. 5 (a)).In Figure 11, during the power failure wherein the load current level on the two-phase be before the fault level 50%, be 100% on third phase.Curve among Figure 12 shows the operating characteristics of a power failure period three load side directivity element.The B-C phase polarizing voltage of A-phase directional relay is zero.In general, this can stop a lot of electromechanics or even the static directional relay directivity of finishing the A-phase measure.But, can use relay comprising under the situation of storage arrangement, polarizing voltage level before the described storage arrangement record trouble (the typical memory duration is about about 3 seconds) therefore just can consider to have the A-phase element operating characteristics of B-C polarizing voltage memory.

As can be seen from Figure 12, C-phase directional relay checking elements may cause the polarizing voltage and the operating current relation of the involuntary maneuver of this relay.If the setting of load side directional relay electric current is lower than 50% of fault preload current level, then this involuntary maneuver just may.From this figure as seen, for unity power factor load condition considered here, A-phase directional relay is restricted.Concerning lagging power-factor or even a little the leading power factor load, also have restriction.The leading load power factor of needs＜0.867 produces the boundary condition that makes the action of A-phase directional relay, and this can constitute extremely insecure condition.

When considering the standard design criterion of parallel feeder previously discussed, one of feed line out of service and must the carrying maximum system when load, the minimal security electric current of directional relay is set to 25% of rated current on two parallel feeders, is 33% of rated current concerning three feed lines.

As previously mentioned, the inventor has had realized that the unexpected potential problems of those skilled in the art, if promptly do not realize the specific action current threshold, power failure can cause the involuntary maneuver of directional relay at the load bus end.Even to this day, this problem is covered by two common condition: the first, and the very low electric current setting of general use seldom; The second, seldom met the peak load that stream is protected feed line.Even when fault current was provided with threshold value just over minimal security, the application of relay characteristic usually caused having before the relay actual act enough relay response times to remove fault during change.But this just situation is for some local electric power system in the world, even the shortage of power plant may mean that each feed line in the parallel feeder group is also all loaded near the full capacity when all coming into operation in all power plant.Under this situation, adopt about aforementioned transformer feed line rated current 85% (being rated for 86.7%) or the minimum directional relay electric current setting of common feed line about 50% is very necessary.The criterion that relay especially must be observed when adopting these to become makes time of this relay malfunction less than the checkout time of power failure.

In another aspect of this invention, provide a kind of interchangeable method to observe the criterion of above-mentioned restriction current threshold.This relates to the application that 3-phase system, 3 is got 2 (2-out-of-3) logic device, make when only in three directional relays that from the 3-phase system, exist, having two to move and required their separately circuit breaker trips, just from circuit, withdraw from a feed line part.The basic principle of this method can find out that obviously, under the misoperation state that is caused by power failure, three directional relays that are used for three-phase have only an actuating of relay from Fig. 9 and 12.In these two figure, this relay is the C-phase relay.Yet when fault appeared at the power supply downstream, this situation should be moved with regard to the desired orientation relay, should move with the directional relay that two-phase is relevant at least.

3 hardware of getting 2 (2-out-of-3) level implement to see Figure 13.In Figure 13, the output (22-A, 22-B, the 22-C of say so more accurately three-phase A, B, C) of the directional relay 22 relevant with first parallel feeder 20 introduce separately with door 93, their output is used to make circuit breaker 95 tripping operations separately.Identical relay input also is introduced into 3 and gets 2 grade 91, and the output of this grade is as importing with the common activation of door 93.Similarly situation is applicable to second feed line 30.

In the action, when any two actions were arranged in any two or three relays 32 are arranged in three directional relays 22, what be used for specific feed line gave circuit breaker 95 and 96 separately with the door transmission from the trip signal of those relays that moved.But under above-mentioned situation at power failure, because each feed line only has an actuating of relay, inoperative and door, relevant circuit breaker just can not trip.

Certainly, logic function in fact shown in Figure 13 also can realize with software, and realize without hardware.

Claims (7)

1. avoid one or more directivity overcurrent protection relays (22; 32) device of involuntary maneuver; described relay is arranged on a plurality of parallel feeders (20 of polyphase ac electric power system; 30) each phase (A of each feed line; B; C) in; described feed line is fed and is presented load successively from AC power (10); relay (22; 32) be positioned at described feed line (20; 30) power circuit of described power supply (10) is pointed in load side and response, it is characterized in that, only just comes into force when another relay in mutually also is in the same action state at least at the operate condition of a phase repeat circuit.

2. device according to claim 1 is characterized in that described AC system is a three-phase system, and for each feed line (20,30), described device comprises from what the relay relevant with that feed line output was presented 3 gets 2 determination devices (91).

3. device according to claim 2 is characterized in that relay is an electrotimer.

4. device according to claim 2 is characterized in that, relay when relay is change.

5. be included in a plurality of parallel feeders (20 of polyphase ac electric power system; 30) each phase (A of each feed line; B; C) the directivity overcurrent protection relay (22 in; 32); feed line is the transformer feed line of feeding from AC power (10) and successively to the load power supply; relay (22; 32) be positioned at the described feed line (20 of transformer secondary separately; 30) power circuit of described power supply (10) is pointed in load side and response; it is characterized in that the minimum that is provided with of the minimal security operating current level of relay is about 85% of the rated load electric current relevant with described feed line.

6. relay according to claim 4 is characterized in that, described minimal security operating current level be made as the rated load electric current 86% and 87% between.

7. relay according to claim 4 is characterized in that, described minimal security operating current level is made as 86.7% of rated load electric current.

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