GB/T 24842-2018Overvoltage and insulation coordination of 1000kV UHV AC transmission project (English PDF)

3.1 Ground flash density

The number of ground lightnings per square kilometer per year.

3.2 Protection angle

The angle between the vertical plane of the ground wire and the ground wire and the outer sub-wire plane protected by lightning strikes.

3.3 Very fast transient overvoltage

Isolation switch operation or ground fault of gas insulated metal-enclosed switchgear (GIS) and composite electrical appliance (HGIS, Hybrid-GIS) At the time, the generated frequency is a high-frequency oscillation overvoltage of several hundred kHz to several tens of megahertz.

3.4 Representative overvoltage

Assume that the effect produced by the insulation is equivalent to the effect of a given type of overvoltage generated by the system for different reasons during operation. Overvoltage. In this standard, representative overvoltage is generally obtained by simulation calculation.

3.5 VFTO damping busbar

The busbar section that is inserted into the busbar circuit to reduce the steepness of the traveling wave of the VFTO has a large inductive reactance value under the action of VFTO, during normal operation. The power frequency inductance is small and negligible.

5.1 System Grounding Method

The 1000kV system adopts an effective grounding method, and does not allow the neutral point of the 1000kV transformer to be grounded.

The low voltage side (110kV) of the 1000kV transformer is ungrounded.

5.2 Type of action voltage

Substation equipment and lines may be subjected to operating voltages in accordance with the cause and magnitude, waveform and duration of the applied voltage. It can be divided into.

a) continuous operating voltage (the value does not exceed the system maximum voltage Um, the duration is equal to the operating life of the equipment design);

b) temporary overvoltage (including power frequency overvoltage, resonant overvoltage);

c) operation (before wave) overvoltage;

d) lightning (fast wave front) overvoltage;

e) Very fast transient overvoltage (VFTO).

See Appendix A for typical waveforms for various types of applied voltages.

5.3 Temporary overvoltage and reference voltage for operating overvoltage threshold

The reference voltage of the power frequency overvoltage is Um/3; the reference voltage for the resonant overvoltage and the operating overvoltage is 2Um/3.

6.1 Temporary overvoltage type

Temporary overvoltages include power frequency overvoltage and resonant overvoltage, and system structure, capacity, parameters, operating mode, ground wire type and grounding The mode and the relay protection and the characteristics of the automatic adjustment device are related. Power frequency overvoltage, resonant overvoltage, in addition to increasing the voltage required for insulation In addition, it also has an important influence on the parameters of overvoltage protection devices such as lightning arresters. Temporary overvoltage characteristics due to its amplitude, waveform and duration determine.

6.2 Power frequency overvoltage

6.2.1 Power frequency overvoltage is mainly caused by line no-load, load shedding and ground fault. Under normal circumstances, both load shedding and ground faults The power frequency overvoltage caused by the combination is more serious. For power frequency overvoltage, it should be predicted in combination with engineering conditions.

6.2.2 Predict the power frequency overvoltage, mainly consider the following types of faults.

a) For single-circuit transmission lines, the load rejection under normal transmission conditions and the load rejection in the case of single-phase ground faults are usually considered. barrier. The probability of a single-phase two-phase grounding causing a three-phase tripping at one end of the line is small, and may be considered as appropriate.

b) For double-circuit transmission lines on the same tower, it is necessary to consider the operation of double-circuit line operation and one-line line stop operation. Double-circuit line with the same name or different name The probability of a phase-to-earth fault is small, and the load shedding in this fault condition can be considered as appropriate. Double-circuit line 6 phase load rejection can be discretionary consider.

6.2.3 The main measure to limit the power frequency overvoltage is to install a line high voltage shunt reactor.

6.2.4 The duration of the power frequency overvoltage plays an important role in the selection of the rated voltage of the arrester and the insulation capacity of the equipment. In order to shrink For the duration of short power frequency overvoltage, the circuit breakers at both ends of the line should adopt relay protection to realize linkage linkage.

6.2.5 The power frequency overvoltage level should not exceed the following values.

a) 1.3 pu on the substation side of the line breaker (duration is not more than 0.5 s);

b) The line side of the line breaker is 1.4 pu (duration is no more than 0.5 s).

6.3 Resonant overvoltage

6.3.1 Reasons for the cause

Resonant overvoltages include linear resonance, nonlinear (ferromagnetic) resonant overvoltage, and parametric resonance. With large capacitive components (long line, series complement Compensating the circuit and switching the inductive component (transformer, shunt reactor) with nonlinear excitation characteristics (or as a result of load shedding) A resonant overvoltage can be generated due to linear resonance and ferromagnetic resonance. Preventive measures should be taken to avoid the condition of resonant overvoltage or relay protection The guard limits its amplitude and duration. Resonant overvoltage is usually not considered when selecting the rated voltage or insulation design of the arrester.

6.3.2 Generator self-excitation overvoltage

Under the condition of synchronous engine with capacitive load (such as no-load line), the periodic variation of the generator inductance parameter does not match the system capacitance parameter. At that time, the generator may cause self-excitation (parametric resonance) overvoltage. The criterion for self-excitation does not occur as shown in equation (1).

WN > QcX*d (1)

In the formula.

WN---the rated capacity of the generator in megavolt-amperes (MVA);

Qc---line charging power (considering the influence of high-voltage shunt reactor and low-voltage shunt reactor), the unit is mega (Mvar);

X*d --- Generator equivalent synchronous reactance standard value (including step-up transformer, based on generator capacity).

When the generator capacity is less than the above value, the single machine with no-load long-line operation should be avoided. For possible generator self-excitation overvoltage Use a shunt reactor or overvoltage protection device to cut off the line.

6.3.3 Non-full phase resonant overvoltage

6.3.3.1 When the line with shunt reactor is in the non-full phase state, it can be broken due to the phase-to-phase capacitive coupling between the healthy phase and the open phase. A non-full phase resonant overvoltage is caused on the open phase.

6.3.3.2 A grounding reactor is connected to the neutral point of the high voltage shunt reactor to effectively prevent this overvoltage. Grounding reactor The reactance value should be selected according to the principle of close to the phase-to-phase capacitance of the fully compensated line. At the same time, the requirement of limiting the submerged current should be considered and the parallel connection should be considered. Reactor neutral point insulation level requirements. For the double-circuit line on the same tower, the coupling between the loops will affect the choice of the reactance value of the grounding reactor.

6.3.3.3 When calculating the non-phase-to-phase resonant overvoltage, the following factors should be noted.

a) the difference between the design value of the line parameter and the actual value;

b) deviation between the impedance design value of the high voltage shunt reactor and the grounding reactor and the measured value;

c) Grid frequency change in fault condition.

6.3.4 Resonant overvoltage of no-load transformer

6.3.4.1 The transition process of the no-load transformer operation causes the transformer core to be magnetically saturated, causing the magnetizing inrush current and periodically changing the inductance. When the excitation inrush current harmonic frequency matches the natural vibration frequency of the system, a higher harmonic resonance overvoltage may be generated, and the overvoltage should be given prediction.

6.3.4.2 The operation mode and operation mode of harmonic resonance should be avoided as much as possible. The circuit breaker is equipped with a closing resistor to help reduce the load change The overvoltage amplitude and magnetizing inrush current of the voltage regulator are related to the system characteristics under different operating modes. Overvoltage protection is available To shorten the duration of the resonant overvoltage of the no-load transformer.

7.1 Operating overvoltage level limit

The maximum relative statistical operation overvoltage along the line should not be greater than 1.7 pu.

The maximum relative statistical operation overvoltage of the substation should not be greater than 1.6 pu, and the maximum interphase statistical operation overvoltage should not be greater than 2.9 pu.

For operating overvoltages, it should be predicted in conjunction with engineering.

7.2 No-load line closing and single-phase reclosing overvoltage

7.2.1 Prediction conditions

7.2.1.1 No-load line closing, single-phase reclosing will generate operating overvoltage. Operating overvoltage amplitude depends on a variety of factors, including circuit breakers Type (with or without closing resistor, phase selection closing device, etc.), system characteristics of the power supply side of the closing line, closing line length and reactive power compensation.

7.2.1.2 Predicting the closing voltage of the line closing operation overvoltage The following control conditions are available.

a) The no-load line is closed by the isolated power supply, and the voltage along the line after the line is closed should not exceed the maximum voltage of the system;

b) By the substation connected to the system, the no-load line is closed, and the substation bus voltage before the line is closed is the mother in the corresponding operation mode. The actual voltage of the line, after the line is closed, the voltage along the line should not exceed the maximum voltage of the system.

7.2.1.3 The single-phase reclosing overvoltage is generally not higher than the no-load line closing overvoltage. For special system structures, such as smaller capacity In the power supply system, the single-phase reclosing overvoltage of the longer line may be higher than the no-load line closing overvoltage.

7.2.1.4 For the double-circuit line on the same tower, the single-phase reclosing overvoltage after the single-phase ground fault of the single-circuit line is mainly considered. Double back with the same name The phase-to-phase reclosing overvoltage in the case of a phase-to-phase fault may be higher than the single-phase reclosing overvoltage after a single-phase single-phase ground fault, but The probability of occurrence is extremely low.

7.2.2 Main restrictions

The main measures to limit the over-voltage of line closing and single-phase reclosing, one is to use a closing resistor for the circuit breaker; the other is to install metal oxide to avoid Lightning device. Measures such as phase selection and closing can also be used. For shorter UHV lines, it is possible to determine whether to cancel the circuit breaker after overvoltage calculation. Closing resistor.

7.3 Single-phase ground fault overvoltage

The overvoltage appearing on the sound phase when the line is single-phase ground fault mainly refers to the relative overvoltage, and the phase overvoltage can be neglected.

The magnitude of the ground fault overvoltage is related to factors such as the length of the line and the location of the fault point.

7.4 Fault Clearing Overvoltage

7.4.1 Faulty line sound phase overvoltage

The overvoltage is the single-phase grounding of the line, and the overvoltage generated on the sound phase of the faulty line after the circuit breaker on both sides of the fault phase is opened, The amplitude is lower.

7.4.2 Overvoltage of adjacent lines

This overvoltage is the ground fault of the line fault, after the line circuit breaker on both sides of the fault phase is opened, the direct adjacent or indirect adjacent line in the fault line Overvoltage generated on.

As the number of phase failure phases increases, the overvoltage amplitude tends to increase. Generally consider the conditions of single-phase ground faults to predict and As a design condition for the project. For two-phase short-circuit, two-phase or three-phase ground fault with low probability of occurrence, it can be taken according to the prediction result Restrictive measures.

7.4.3 Single-phase grounding three-phase trip overvoltage

In the case of live working, if the single-phase reclosing is exited, single-phase grounding will cause three-phase opening. Single-phase ground fault, single-phase reclosing is not successful Will cause three-phase opening.

When single-phase grounding three-phase opening, a high overvoltage may occur on the healthy phase or adjacent line of the faulty line.

7.4.4 Fault Clearing Overvoltage and Restrictive Measures

The substation and the switchyard are protected by lightning arresters. The fault clearing overvoltage is not high and will not damage the equipment in the station. For higher faults on the line To remove the overvoltage, a metal oxide surge arrester can be installed in the middle of the line or a tripping resistor can be placed on the circuit breaker to limit it. In addition, restrictions on relay protection can also be used.

7.5 No fault load shedding overvoltage

The faultless load shedding voltage is related to the line length, line reactive power compensation and line current, etc. Limitation.

7.6 Oscillation Dissociation Overvoltage

De-column in the system oscillation state will generate an oscillation-dissolved overvoltage.

The overvoltage under the oscillation decoupling operation may be predicted. When predicting the overvoltage, the power transmission angle of the line transmitting and receiving end should be poor. Select according to the serious conditions that may occur in the system.

Attention should be paid to the absorption energy of the metal oxide arrester at both ends of the calibration line.

7.7 Switching the no-load transformer operating overvoltage

The operating overvoltage generated by switching the no-load transformer is generally limited by the metal oxide arrester.

7.8 Main transformer 110kV side breaking shunt capacitor bank overvoltage

The 110kV side of the main transformer breaks the shunt capacitance compensation device. If the circuit breaker has single-phase heavy breakdown, the capacitor group can over-voltage to ground. Can exceed 4.0 pu. This overvoltage will be higher when there is a single phase ground fault on the power supply side before the break. If two-phase heavy breakdown occurs at the time of breaking, the capacitor The inter-electrode overvoltage may exceed 2.52Un.C (Un.C refers to the rated voltage of the capacitor bank).

Switching parallel capacitor compensation devices should use circuit breakers with extremely low breakdown probability. For safety reasons, it is still appropriate to arrange as shown in Figure 1. Install a metal oxide arrester to the high voltage end of the capacitor bank. To limit single-phase slamming through voltage. Generally, circuit breakers are not considered. Two-phase heavy breakdown occurred.

7.9 Main transformer 110kV side breaking shunt reactor overvoltage