abstract

1. Design Description

1. 1 main wiring

1.2CT, PT configuration

2. Main protection principles and settings ........................................................................................................................................................................

2. 1 generator differential protection ............................... 3

2. 1. 1 protection principle

2. 1.2 Settings

2.2 Generator stator turn-to-turn protection

2.3 generator over-excitation protection

2.4 generator loss-of-excitation protection

2.5 generator inverse time negative sequence overcurrent protection ......................................................... 10

2.6 generator reverse power protection ................... 13

2.7 The generator is grounded at two points: ................................................ 13.

2.8 main transformer differential protection ............................ 14

2.9 transformer compound voltage overcurrent protection .......................................................................................................................................... 65438+ 17

Refer to ......................... 18.

1 design description

1. 1 main wiring

The main protection principle design of 300MW generator-transformer unit is suitable for the generator-transformer unit with 500kV 1 1/2 wiring system connected to the high voltage side. There is no circuit breaker at the generator outlet side; The excitation mode is static excitation system;

A high voltage service transformer (using a three-phase split coil) is connected to the generator outlet side.

Grounding mode: the generator neutral point is grounded through the distribution transformer (secondary side resistance); The neutral point on the high voltage side of the main transformer is directly grounded; The neutral point at 6kV side of high-voltage auxiliary split transformer is medium resistance grounding system.

1.2 current transformer and voltage transformer configuration

Four groups of current transformers are respectively installed on the outlet side and the neutral side of the generator;

Three groups of current transformers are installed on the high-voltage side bushing of the main transformer;

Four groups of CT are installed on the high-voltage side bushing of the high-voltage auxiliary transformer (or in the closed bus);

Generator differential protection and main transformer differential protection, when the CT distribution is not enough, allow * * * to use a set of CT at the generator outlet side;

In the generator-transformer differential protection, one arm is connected to the CT of the low-voltage side of the high-voltage auxiliary transformer.

Generator-transformer differential protection device is not connected with CT of excitation transformer, and its differential range is: from 500kV side CT to generator neutral point CT and low voltage side CT of high voltage auxiliary transformer;

Secondary current of current transformer:1a; 500kV side selection; Other faces can be 1A or 5A.

There are two groups of PT on the generator outlet side, of which 1 group can be used for turn-to-turn protection (the neutral point on the primary side is not directly grounded); Two sets of PT require three secondary coils. 1 PT (three-phase) is set on the high voltage side of the main transformer.

2 main protection principle and setting calculation

2. 1 generator longitudinal differential protection

2. 1. 1 protection principle

Braking principle of scalar product with variable data window

∣IT-IN∣2≥KbITINcosφ

Where: it- generator terminal current

Neutral point current in generator

φ ―― phase angle difference between it and iN

The action quantity of scalar product braking principle is the same as that of ratio differential protection When a fault occurs outside the area, the performance behavior of this principle is exactly the same as that of the proportional braking principle. However, when a fault occurs in the area, the braking amount of scalar product braking principle reflects the cosine of the phase between currents. When the phase is greater than 90 degrees, the braking amount becomes negative, and the negative braking amount is conceptually the action amount, so the sensitivity of protection response can be greatly improved when an internal fault occurs. The braking amount of the ratio braking principle is always greater than 0.

Action logic mode 1: loop locking mode.

Principle: When the generator is short-circuited between phases, two-phase or three-phase differential will act at the same time. According to this feature, a cyclic locking mode is designed in the protection tripping logic. In order to prevent the occurrence of two-point grounding fault with one point in the area and the other point outside the area, when there are differential and negative sequence voltages at the same time, the outlet also trips.

2. 1.2 setting content (assuming that the secondary rated current of TA is 5(A))

1) ratio braking coefficient k

Set the ratio braking coefficient of differential protection. Kb and k of scalar product braking principle have a corresponding relationship in theory. Devices automatically complete the conversion between them and still set K for users. No unit. General: k = 0.3-0.5

2) Starting current lq

Set the starting current of differential protection. Unit (a). Generally lq=0.6-2.0(A)

3) TA disconnection unlocking current setting value (only valid in protection mode II) lct

When the generator differential current is greater than the fixed value, the TA disconnection locking function automatically exits. Unit (times)

It is based on the secondary rated current of current transformer. In general: lct=0.8- 1.2 (times)

4) Differential quick-break multiple lsd

When the generator differential current is greater than the fixed value, the differential will act regardless of the braking amount. Unit: (times)

It is based on the secondary rated current of current transformer. General: LSD = 3-8 (times)

5) negative sequence voltage setting value (effective only in protection mode Ⅰ) U2.dz

When the negative sequence voltage reaches a fixed value, the differential outlet is allowed to trip. Unit (5). General: U2.dz = 4- 10 (v)

6)TA disconnection delay setting tct

After a fixed delay, the TA disconnect signal is sent. Unit: seconds.

2.2 Generator stator turn-to-turn protection

2.2. 1 principle

The fundamental component reflecting the longitudinal zero sequence voltage of the generator. The "zero sequence" voltage is taken from the open delta winding of the special voltage transformer at the machine end. This transformer must be of three-phase five-column type or three-phase single-phase type, and its neutral point is connected with the generator neutral point through high-voltage cable. Using digital Fourier filter to filter out the third harmonic imbalance in zero sequence voltage.

In order to accurately and sensitively reflect the internal turn-to-turn fault and prevent the protection from misoperation when the external short circuit occurs, this scheme distinguishes the internal fault from the external fault by the change of the third harmonic characteristic in the longitudinal "zero sequence" voltage.

In order to prevent the protection from misoperation when the special voltage transformer is disconnected, the scheme adopts a reliable voltage balance relay as the disconnection locking link of the transformer.

This protection can respond to the open welding fault of stator winding with double Y connection under a certain load.

Protection is divided into two parts:

Section I is sub-sensitive: the action value must avoid the fundamental imbalance that may occur when any external fault occurs to protect the instantaneous exit.

The second section is the sensitive section: the action value reliably passes through the maximum fundamental imbalance during normal operation, and the change of the third harmonic imbalance in the "zero sequence" voltage is used for braking. The protection can exit with a delay of 0. 1-0.5 seconds to ensure reliability.

Protect the zero sequence voltage introduced into the open triangle winding of special voltage transformer and two groups of PT voltages of voltage balance relay.

2.2.2 Setting content

1) Fixed value of "zero sequence" voltage component of fundamental wave in secondary sensitive section Uh unit (V)

2) Fixed value of "zero sequence" voltage component of fundamental wave in sensitive section U 1 unit (V)

3) Setting value of third harmonic unbalance of "zero sequence" voltage under rated load U3wn unit (V)

4) Third harmonic incremental braking coefficient K2 in sensitive section Unit: (None)

5) Tzj unit of sensitive section delay: (seconds)

2.2.3 setting calculation

1) mm-hmm

Fixed value of fundamental component of "zero sequence" voltage in secondary sensitive section (setting range 1- 10V)

The action value is set according to the fundamental imbalance that may occur when avoiding any external fault.

Er = wide? bp？ maximum

Among them: Er = Guo? bp？ Maximum possible "zero" in case of external short circuit fault.

Maximum fundamental unbalance of sequence voltage.

K- reliability coefficient, preferably 2-2.5.

2)U 1

Fixed value of fundamental component of "zero sequence" voltage in sensitive section (setting range 0. 1-5V)

The action value is set according to the maximum fundamental imbalance that can be reliably avoided during normal operation.

U 1=KUo？ bp？ n

Where: U 1=KUo? bp？ N―― Inherent "zero sequence" voltage basis under rated load

The wave unbalance is measured (this machine has monitoring software).

K- reliability coefficient, which can be 1.5-2.

3)U3wn

Setting value of third harmonic unbalance of "zero sequence" voltage under rated load (setting

Range 1- 10V)

You can set 4(V) at the beginning, get an accurate straight line from the actual measurement after starting, and then set it.

4)

Third harmonic incremental braking coefficient in sensitive section (set range 0-0.9)

Determined by experience. Generally take 0.3-0.5.

5)Tzj

Sensitive segment delay (setting range 0- 1 sec)

Aiming at increasing the reliability of this part. It usually takes 0. 1-0.2 seconds.

2.3 generator (transformer) over-excitation protection

principle

Generator (transformer) will be over-excited due to voltage increase or frequency decrease, and the over-excitation ability of generator is lower than that of transformer, so the over-excitation characteristics of generator-transformer protection should generally be set according to the characteristics of generator.

Over-excitation protection responds to over-excitation multiple action. Overexcitation multiple is defined as follows:

B U/f U*

N= = =

Be Ue/fe f*

Where: u, f- voltage, frequency

Ue, Fe- rated voltage and rated frequency

U*, F *- unit values of voltage and frequency.

B, be- magnetic flux and rated magnetic flux

Overexcitation voltage is taken from TV line voltage at the machine end (such as UAB voltage).

Export mode ⅰ: fixed time limit mode

T 1 send letters or trip regularly.

Send a message or trip at a fixed time t2.

u/f & gt； T 1/o send or trip.

T2/ Output signal or trip

Derived Mode Ⅱ: Inverse Time Mode

Fixed time limit letter sending

Inverse time transmission or tripping

The characteristics of the inverse time limit curve are composed of three parts: a) upper limit time limit; B) inverse time limit; C) set a time limit.

When the over-excitation multiple of the generator (transformer) is greater than the upper limit setting value, act according to the upper limit time; If the multiple exceeds the lower limit set value, but it is not enough to make the inverse time limit part act, it will act according to the limited time limit; The middle multiple acts according to the law of inverse time limit.

2.4 generator loss-of-excitation protection

2.4. 1 principle

Loss-of-excitation protection consists of generator terminal measurement impedance criterion, rotor low voltage criterion, transformer high voltage side low voltage criterion and stator overcurrent criterion. Generally speaking, the impedance setting boundary is a static boundary circle, but it can also be other shapes.

When the generator needs leading phase operation, if the circle set according to the static boundary cannot meet the requirements, generally one of the following three ways can be adopted to avoid the leading phase operation area.

A) Move down the impedance circle and set it according to the asynchronous boundary.

B) Use two straight lines passing through the origin to avoid the phase entry area. At this time, the phase advance depth can be adjusted.

C) Excavate the possible phase lead area (circular feature) to avoid the phase lead area.

Rotor low voltage action equation

Vfd & ltVfl.dz Vfd & ltVfl.dz

Vfdo

VFD & lt(P-Pt) when VFD.

Kf×SN

Where: VFD- rotor voltage

Vfl.dz―― Low voltage operation value of rotor

VFDO- generator no-load rotor voltage

Sn- rated power of generator

Kf―― Low voltage coefficient of rotor

P- generator output

Pt- generator reaction power

2.4.2 protection setting calculation

1) Low pressure Uhi at high pressure side? Domain name of Algeria

The display system allows low voltage settings for long-term operation.

2) impedance center -Xc

Static stable circle or asynchronous circle can be used for fixing.

3) radius of impedance circle -Xr

Static stable circle or asynchronous circle can be used for fixing.

4) Rotor low voltage Vfl? Domain name of Algeria

The low voltage of the rotor can be set to 0.2-0.5 times the no-load excitation voltage of the generator.

5) Criterion coefficient Kf of rotor low voltage

Rotor low voltage coefficient, which is used to set the slope of rotor voltage action curve. Unit (yuan)

Qiankai

Kf = where xd ∑ = xd+xs.

Xd∑

If the actual benchmark is Vfd[0] and P[0], which is quite different from the assumed values VFD 0 = 125V and Sn = 866VA, Kf can be corrected.

125 P[0]

[Integer] = Kf

866 Vfd[0]

Xs is the sum of the equivalent reactances of the step-up transformer and the system (unit)

KK = 1. 1 is the reliability coefficient and Xd is the generator reactance (standard).

5) reaction power Pt

Consider the salient pole effect. Unit (Watt)

1 1 1

Pt = (-)SN, where: xd ∑ = xd+xs, xd ∑ = xq+xs.

2 Xq∑Xd \

Xd and Xq are reactances (units) of D-axis and Q-axis of generator respectively, and SN is secondary reference power.

7) stator overcurrent lg? Domain name of Algeria

Can be set according to the overload asynchronous power of the generator. Unit (a). General lg? Dz= 1.05 le

8) Action time t 1

Set the delay action time of protection. unit

9) Action time t2

Set the delay action time of protection. unit

10) action time t3

Set the delay action time of protection. unit

2.5 generator inverse time negative sequence overcurrent protection

2.5. 1 protection principle

Protect the negative sequence current of generator stator. Prevent the generator rotor from overheating.

The protection consists of negative sequence definite time overload and negative sequence inverse time overcurrent.

The current is taken from the generator neutral point (or machine end) TA three-phase current.

The characteristics of the inverse time limit curve are composed of three parts: a) upper limit time limit; B) inverse time limit; C) set a time limit.

When the negative sequence current of the generator is greater than the upper limit setting value, act according to the upper limit time limit; If the negative sequence current exceeds the lower limit setting value, but it is not enough to make the inverse time limit part act, it will act according to the limited time limit; In the meantime, the negative sequence current acts according to the law of inverse time limit.

The negative sequence inverse time-limit characteristic can truly simulate the heat accumulation process and heat dissipation process of the rotor, that is, if the negative sequence current disappears after the generator heats up, the heat accumulation will not disappear immediately, but will slowly dissipate heat, so that the negative sequence current will increase again, and the last heat accumulation will become the initial value of this time.

Agenda for action against time:

(I22-K22)t≥K2 1

Where: I2-unit value of negative sequence current of generator.

K22―― The heat dissipation effect of the generator when heating.

K21-a value of the generator

Exit mode: it can send letters or trip.

2.5.2 protection setting calculation

1) Fixed time negative sequence overload current setting I2? ms？ Domain name of Algeria

According to the condition that the generator can return reliably under the long-term allowable negative sequence current.

2) definite time limit negative sequence overload action time ts

According to the action delay setting of backup protection.

3) Inverse time negative sequence overcurrent start setting I2? m？ Domain name of Algeria

According to the maximum tripping time provided by the protection device (usually 1000 second), the negative sequence current that the generator can bear is set accordingly. This value should generally be close to the action current of negative sequence overload protection.

4) Inverse time negative sequence overspeed judgment value I2? Up? Domain name of Algeria

Set according to the condition of avoiding two-phase short circuit on high voltage side of main transformer.

5) Heat dissipation coefficient K22

Generally, it is set according to the unit value of negative sequence current allowed by the generator for a long time.

K22=(I2∝/ Ie)2

When the actual rated current of the generator is Ie, which is quite different from the CT secondary rated current IN, it needs to be converted.

Pragmatic trade (labor exchange) low explosive (labor exchange)

K22[ integer] =( )2 K22

lN

Pragmatic trade (labor exchange) low explosive (labor exchange)

K2 1[ integer] =( )2 K2 1

lN

Where: L2∝- Long-term allowable negative sequence current of generator.

Rated current of generator

6) calorific value coefficient K2 1

According to the generator a value.

7) Long delay action time t 1

Press l2? m？ Setting of the time that dz current can withstand (generally 1000 second).

8) Quick-break action time chart

When there is a contradiction with other protections in the coordination of action time, the selectivity and sensitivity requirements of protection should be considered.

2.6 generator reverse power protection

Protection principle

Reverse power protection is used to protect the steam turbine. When the main valve is closed by mistake, or the unit protection action closes the main valve without tripping the outlet circuit breaker, the generator will be converted into a motor to absorb active power from the system. At this time, due to blast loss, the turbine tail blade may overheat, which is beneficial to turbine damage. Therefore, this situation is generally not allowed to exist for a long time, and reverse power protection can play a very good protective role. Generally, two sets of independent reverse power protection are installed on large generator sets to ensure reliability.

The reverse power protection reflects the active power absorbed by the generator from the system. The reverse power supply is blocked by the TV disconnection.

The voltage is taken from the generator end; The current is taken from the generator neutral point (or machine end) ta.

Exit mode: it can send letters or trip.

P & lt-P 1.dz t 1/o sends information or trips.

T2/ Output signal or trip

2.7 generator rotor two-point grounding protection

It reflects the "positive sequence" component of the second harmonic in the stator voltage. When the rotor winding is asymmetrically short-circuited, the magnetic field containing the second harmonic rotates forward at the synchronous speed, which produces this component in the stator winding. The protection is locked by one-point grounding protection, and the protection is automatically put into operation when one-point grounding occurs.

Protect the three-phase voltage at the machine end.

8.6. 1 Settings

1) secondary wave voltage action value Uido unit: (v)

2) protection action delay Tido unit: (s)

8.6.2 Setting calculation method

1)Uid

Second harmonic voltage action value (set range 0- 10V)

Uld=Kk×Ubpn

Ubpn is the measured value of the second harmonic voltage under rated load; Kk is the reliability coefficient, 2.5-3.

2) Doctor of Law

Protection action delay (setting range is 0. 1-2 seconds) to increase reliability.

2.8 Differential protection of main transformer (generator transformer group, auxiliary transformer and high standby transformer)

Protection principle

The transformer differential protection adopts the ratio differential principle with second harmonic braking and the fast algorithm with variable data window.

Ratio braking principle

∣ i 1+I2 ∣≥ kmax {i 1, I2} (bilateral difference)

∣ I1+I2+i3∣≥ kmax {I1+I2+i3} (Trilateral Difference)

Where: I 1- first side current

I2―― Current on the secondary side

I3―― Current at the third side

K- braking coefficient

Max (x, y)- take the maximum of x and y.

Principle of variable data window algorithm

The so-called variable data window algorithm means that differential protection can adaptively improve the braking curve of protection at the beginning of fault, and the amount of fault sampling data is small. With the further development of the fault and the further improvement of the calculation accuracy, the braking characteristic curve can be reduced every turn, which is completely compatible with the accuracy of the algorithm. This adaptive braking curve is the final (and most accurate) feature set by users. Using this algorithm can greatly improve the action speed when the internal fault is serious, and at the same time, it will not reduce the sensitivity when the internal fault is slight.

Export mode

Principle: Any differential protection action is an export trip. This method also adds the function of TA disconnection detection. When TA is disconnected, the differential protection will be locked instantly, and the TA disconnection signal will be delayed. TA disconnection can be switched back and forth as needed. protective

8.7.2 Setting content (assuming that the secondary rated current of TA is 5(A))

1) ratio braking coefficient k

Set the ratio braking coefficient of differential protection. Unit (None) General: K=0.4-0.7

2) Second harmonic braking ratio

Set the differential second harmonic braking ratio. Unit (None). General:

Nec=0. 12-0.24

3) Starting current lq

Set the starting current of differential protection. (Back to the low pressure side). Unit (a). General: lq= 1.0-3.0(A)

4) TA disconnection unlock current constant value lct

When the differential current is greater than the fixed value, the TA disconnection locking function automatically exits. Unit: (times)

It is based on the secondary rated current of TA. (The default value inside the device is 5(A) or 1(A).

Generally: lct=0.8- 1.5 (times). (Return to low pressure side)

5) quick break current lsd

Set the quick-break current multiple of differential protection. It is based on the secondary rated current of TA. (The default value inside the device is lN5(A) or 1(A))

Unit (times). General LSD = 3.0-7.0 (times) (reduced to low voltage side)

6) Starting current lq

According to the unbalanced current flowing into the protection device, the action of the protection device is controlled under the condition of avoiding the maximum load current. The minimum working current should be higher than 0.2ls.

Generally speaking, the device is set by reducing the current to the low voltage side (such as the generator side).

7) TA disconnection unlock current constant value lct

According to avoid the maximum load current setting of transformer.

Current devices are generally set and calculated by reducing the current to the low-voltage side (such as the generator side).

It is based on the secondary rated current of TA.

Ict =( 1.2- 1.3) What if? max/(nL×Ict？ e)

Where: if? Maximum-maximum load current of transformer

Ict？ E- secondary rated current of current transformer

8) Quick-break current lsd

Current devices are generally set and calculated by reducing the current to the low-voltage side (such as the generator side).

It is based on the secondary rated current of TA.

If the rated current is set to n times, the secondary rated current of TA is 5(A):

Then: LSD = n× le/(n 1× 5) (times)

N recommends 4-8.

2.9 Transformer Composite Voltage Overcurrent Protection

principle

Protection reaction transformer voltage, negative sequence voltage and current.

Current and voltage are generally taken from the same side of transformer TA and TV.

Exit mode: it can send a letter or travel.

Set content

1) current setting lg? Domain name of Algeria

Set the current. Unit (a)

2) low voltage cutoff value U 1? Domain name of Algeria

Set the low voltage. Unit (5)

3) Negative sequence voltage setting value U2? Domain name of Algeria

Set the negative sequence voltage. Unit (5)

4) Action time t 1

Set the delay action time of protection. unit

5) Action time t2

Set the delay action time of protection. unit

Take the exam and contribute.

[1], principle and application of microcomputer, Zheng, editor. Tsinghua University Publishing House,1August 995.

[4], Malvino. A.P. Digital Computer Electronics. McGraw-Hill Publishing Company, 1977.

[2] A.R. van.C. Warrington. Protection relay, vo. One-two. 1974.

[3], Committee report, transient response of current transformer. E.E.PAS,1977.no6.

[4], edited by Ma Changgui, Principles of Relay Protection for High Voltage Power Grid, Water Conservancy and Electric Power Press, 1988.

[5], Xu Zhengya, Power System Fault Analysis, Water Conservancy and Electric Power Press, 1993.

[6], Northwest Electric Power Design Institute, Handbook of Electrical Design for Power Engineering 2, Water Conservancy and Electric Power Press, 1990.

[7], National Electric Power Dispatching and Communication Center, Practical Technical Questions and Answers of Power System Relay Protection, China Electric Power Press,1997,5.

[8], National Power Dispatching Communication Loyalty "Compilation of Power System Relay Protection Regulations", China Power Press, 1997.

[9], Shandong Electric Power Bureau document 1997.

[10], Southeast University, Nanjing Electric Power Automation Equipment General Factory, Technical Specification for WFB2-0 1 Microcomputer Generator-Transformer Protection Device. 1997、4、28

[1 1], Nanrui Relay Protection Company, Dai, "Principle and Technology of Microcomputer Relay Protection"