DL/T 2003-2019Application guide of on-load tap-changer for HVDC converter transformers (English PDF)

4.1 Structure

The on-load tap-changer for the converter transformer is generally a combined on-load tap-changer according to the particular application conditions.

4.2 Arc extinguishing method

The on-load tap-changer for converter transformers is classified into vacuum extinguishing type and oil extinguishing type according to the arc extinguishing mode.

5.1 Basic selection principles

The selection of the on-load tap changer for the converter transformer should meet the principle of the HVDC transmission system and the actual operation and test conditions of the converter transformer.

Priority is given to the use of existing standard on-load tap-changers, generally combined on-load tap-changers. Its structure, function, technical parameters and the installation method shall meet the relevant requirements for the safe operation of the converter transformer. Based on the particularity of the converter transformer, the selection of its on-load tap changer needs to be considered Voltage regulation range, voltage regulation stages, switching load, operating frequency, protection when on-load tap changer is abnormal, harmonic component, current change rate, change Rheological impedance, long-term overload conditions of commutation transformer, gas production requirements for over-polarity conversion, etc.

5.2 Determination of basic parameters

5.2.1 The type and parameters of the on-load tap changer should be selected according to the system and converter transformer parameters, including but not limited to the following information.

a) Type of converter transformer (double winding or triple winding), single rated capacity;

b) Rated voltage, regulation range, voltage regulation stages, impedance voltage;

c) The winding connection mode of the converter transformer, the connection group of the grid side and valve side winding, the number of phases, the number of parallel winding columns and the capacity of each column;

d) Tap winding wiring diagram, winding arrangement size diagram (or necessary tap winding part to ground and capacitance between other windings, coarse and fine adjustment Leakage reactance when windings are connected in series);

e) Maximum level voltage, maximum operating current, zero-crossing change of grid-side winding load current under different trigger angles/turn-off angles of a single converter transformer Rate (di/dt), harmonic spectrum;

f) Switch insulation level;

g) The voltage gradient on the tap winding during the impact test and the AC induction test;

h) The relevant requirements of the power grid system, such as the overcurrent and overexcitation requirements of the converter transformer;

i) Requirements for the on-load tap changer protection system;

j) Requirements for the secondary control system of the on-load tap-changer drive mechanism, including the on-load tap-changer tap position signal and operating status signal.

5.2.2 The manufacturer of the on-load tap-changer shall calculate and determine the appropriate on-load tap-changer based on the information in 5.2.1.

a) The specific model and parameters of the on-load tap changer;

b) Connection diagram and size diagram of on-load tap changer;

c) Potential resistance value, connection diagram and size diagram;

d) Protection device configuration and drawings, and the protection value is determined;

e) Electric mechanism configuration, size diagram and circuit schematic diagram.

The converter transformer manufacturer shall verify the type and technical parameters of the determined on-load tap changer.

5.3 Tap range

The tapping range and the number of voltage regulation stages of the on-load tap changer used in the commutation transformer should fully consider the various operating conditions of the DC transmission system and the operation of the converter.

According to the requirements, the system should be designed with the on-load tap-changer supplier to confirm whether the product meets the requirements.

5.4 Winding arrangement

The conventional layout of main winding and tap winding of converter transformer mainly includes "iron core-valve-net-adjustment-tank" and "iron-core-adjustment-net-valve-tank" Two ways. When selecting the on-load tap-changer, pay attention to the winding arrangement, which is caused by the recovery voltage of the on-load tap-changer when the change-over selector acts.

influences.

5.5 Current rate of change

The on-load tap-changer supplier shall calculate the recovery caused by the current change rate according to the current change rate under different firing angles provided by the system the influence of voltage, circulating current, switching capacity, etc. on the on-load tap-changer, and provide on-load tap-changers that meet the requirements. About current changes refer to Appendix A for the influence of speed on the performance of the on-load tap changer of the converter transformer.

5.6 Extinguishing method

The current rate of change when the load current crosses zero has a greater impact on the breaking performance of the switch contacts. When the commutation transformer is running, its load current is over the zero current rate of change is much greater than the zero-crossing rate of change of a standard AC sine wave. Under the same passing current and voltage level, when the current change rate when it is higher, the switching capacity of the arc extinguishing switch in oil is lower than that of the vacuum extinguishing switch. Should be selected according to the converter capacity and current change rate the arc extinguishing mode of the on-load tap changer. For example, in the application of single-phase dual-column converter transformers with lower capacity, a single dual-pole vacuum arc extinguishing to connect the switch, you can also choose two single-pole arc extinguishing on-load tap-changers; similarly, for single-phase three-column converter transformer applications, you can choose A single three-pole vacuum arc extinguishing on-load tap-changer can also be used with three single-pole oil extinguishing on-load tap-changers. The principle of choosing the arc extinguishing method it depends on the ability of the switch to break with a higher rate of current change.

5.7 Harmonics

The supplier of the on-load tap-changer should consider the selection of the on-load tap-changer's current-carrying and arc extinguishing capabilities under harmonic conditions based on the harmonic current spectrum.

5.8 Potential resistance (binding resistance) and potential resistance switch

The recovery voltage generated by the on-load tap changer selector for the commutation transformer is relatively large, and the tap winding (generally is the middle part) connected to a fixed potential (such as the neutral point) to limit the tap winding potential, thereby limiting the recovery electricity generated when the change-over selector moves Pressure.

The converter transformer has a large voltage regulation range and high level voltage. When the potential resistance is fixedly connected, a large loss will be generated under the action of the tap winding voltage.

In order to reduce the loss, the potential resistance should be connected to the potential resistance switch.

The potential resistance should have sufficient heat capacity. The resistance value is based on the converter variable structure parameters and the on-load tap changer switch selector recovery voltage withstand the value is calculated and determined.

6.1 Overview

The on-load tap changer shall meet the requirements of this chapter in addition to the requirements of GB 10230.1 and GB/T 10230.2.

6.2 Operating conditions

The operating conditions are consistent with the converter transformer.

If the operating conditions of the on-load tap-changer do not meet the operating conditions of the converter transformer, you should consult the on-load tap-changer manufacturer when ordering.

Provide special instructions so that the on-load tap-changer manufacturer can provide corresponding measures or products.

6.3 Overload

The on-load tap-changer shall meet the overload requirements of the converter transformer, and its maximum rated through current shall be considered based on 1.1 times the overload of the converter transformer.

6.4 Mechanical life and electrical life

The arc-extinguishing on-load tap-changer in oil shall not need to be lifted for inspection and repair within 6 years of operation and 100,000 operations. Electricity of switch contacts the service life should not be less than 300,000 times, and the mechanical life should not be less than 800,000 times.

The vacuum arc extinguishing on-load tap-changer should not need to be lifted and repaired within 15 years of operation and 300,000 operations, and the electrical life should not be less than 600,000 times, the mechanical life is not less than 1.2 million times.

6.5 Oil conservator and oil compartment

An independent oil conservator should be installed on the on-load tap-changer. The volume of the oil conservator should meet the operating temperature changes of the on-load tap-changer and regular oil sampling.

At the same time, factors such as the number of parallel units, oil filter and heat sink should also be considered.

The oil chamber of the on-load tap-changer shall be able to meet the requirements of vacuuming simultaneously with the converter oil tank.

6.6 Oil temperature requirements in the oil chamber during continuous operation

During the operation of the on-load tap-changer, the oil temperature in the independent oil chamber of the on-load tap-changer should not exceed 125°C.

If the converter transformer requires continuous operation of the on-load tap changer, it should be mentioned when ordering. Performed by the on-load tap-changer manufacturer according to requirements Check the temperature rise.

6.7 Insulating oil, oil filtering device and heat sink

6.7.1 Insulating oil

The oil in the oil chamber and its oil conservator should use the same oil as the converter transformer body.

6.7.2 Oil filter device

The on-load tap-changer with arc extinguishing in oil should be equipped with an online oil filter device, and its installation position should consider maintenance, replacement of the filter element and observation of the filter element condition the convenience. The on-load tap-changer manufacturer should provide a start-stop strategy plan, and the start-stop of the oil filter device should not cause protection malfunction.

The on-load tap-changer on-line oil filter device should have the function of filtering impurities and moisture (composite filter element or single filter element), and easy to replace the filter element.

When multiple oil-extinguishing on-load tap-changers are used in one converter transformer, each on-load tap-changer should be equipped with an independent online oil filter device.

Set.

The on-load tap-changer of vacuum extinguishing type can not be equipped with online oil filter device.

The independent oil chamber of the vacuum extinguishing on-load tap-changer can be installed with a dissolved gas analysis device in the oil.

6.7.3 Heat sink

According to the requirement of continuous switching times, when the temperature of the oil chamber of the on-load tap-changer exceeds the allowable value, a heat sink should be installed. It and switch on the oil shutoff chamber is connected, and generally consists of oil pump, radiator, connecting pipeline and other parts. The heat sink should effectively control the temperature of the oil chamber, the switch manufacturer should provide start-stop and operation strategies, which should not cause protection to malfunction.

The manufacturer of the on-load tap-changer shall determine the type, specification and control method of the heat dissipation device.

When installing a heat sink, an oil temperature measuring device should be installed at the same time.

6.8 Protection

6.8.1 The independent oil chamber of the on-load tap-changer should adopt an oil flow relay or a pressure relay for converter transformer protection, and no gas with a float should be used.

Body relay. If the on-load tap changer of the converter transformer is only equipped with one of the oil flow relay or the pressure relay, it should be tripped; configure at the same time If the oil flow and pressure relays are activated, the oil flow relay should be tripped, and the pressure relay should be set to alarm. Three sets of independent contacts shall be provided for tripping.

6.8.2 The supplier of the on-load tap-changer shall set appropriate action setting values for its protective relays according to the requirements of the engineering design. Loaded points the factory flow rate setting test of the oil flow relay connected to the switch shall be carried out with the hot oil flow simulating actual working conditions.

6.8.3 When the on-load tap-changer is running in parallel, in order to avoid the on-load tap-changer used in parallel, it may be caused by the gears not being synchronized.

For circulating current, the synchronous operation of the on-load tap-changer should be monitored and control and protection measures should be taken. The on-load tap-changer supplier shall provide Load the tap switch gear signal to the background. When the on-load tap changer positions are not synchronized, the next tap change should be blocked and a signal should be sent to ensure that the Synchronous switching of the on-load tap changer.

6.8.4 In order to prevent the continuous switching operation of the on-load tap-changer from causing excessive oil temperature in the switch oil chamber, the on-load tap-changer can be equipped with an oil temperature measuring device or temperature switch, the supplier should give the oil temperature protection setting value, and the device should have a lock or alarm function.

6.8.5 Other requirements for on-load tap changer protection are implemented with reference to DL ****.

7.1 Type test and routine test

The type, routine test items and requirements of the on-load tap changer shall be in accordance with the relevant regulations of GB 10230.1, JB/T 8314, DL/T 596 carried out. The type, routine test items and requirements of the electric operating mechanism and controller are in accordance with the relevant regulations of GB 10230.1 and JB/T 8314 carried out.

7.2 Routine test with converter transformer

After the converter transformer is assembled, the on-load tap-changer should withstand the following operation test.

a) The converter transformer is not excited, and no less than 8 operating cycles are completed at 100% of the rated operating voltage;

b) The converter transformer is not excited, and one operation cycle is completed at 85% of the rated operating voltage;

c) When the commutation transformer is excited at no load, one operation cycle is completed; the two switches on each side are tapped at the operating position of the changeover selector or in the middle.

Complete 20 tap change operations within a tap range;

d) After the temperature rise test is over, apply the rated current and operate the on-load tap-changer to complete 10 operation cycles. After the test is completed, measure the winding Group DC resistance.

Before, after and 24 hours after the end of the test, the independent oil chamber (only for the vacuum extinguishing switch) and the main oil tank of th...