DL/T 1795-2017Code of operation for VSC-HVDC substation (English PDF)

3.3 STATCOM mode of operation

An operation mode of which the AC side of the VSC-HVDC substation is connected to the AC power grid, while the DC side is electrically disconnected from other substations.

3.4 symmetrical monopolar mode of operation

An operation mode of which the DC circuit potential of the substation is clamped by

AC side neutral point equipment or other equipment; the DC voltage output on the two terminals is symmetrical for a single VSC converter. See Annex A.

3.5 asymmetrical monopolar mode of operation

An operation mode of which the DC voltage output from the two terminals is asymmetrical for a single VSC converter, typically with one terminal grounded. See

Annex A.

3.6 bipolar mode of operation

An operation mode of which two or more VSC asymmetric unipolar circuits form a bipolar DC circuit. See Annex A.

4.1 Operating mode

Based on the connection method between the substation and the AC/DC system, the operating modes are classified as follows.

a) interconnection mode of operation;

b) DC island mode of operation;

c) Static synchronous compensator (STATCOM) operating mode.

According to the DC side wiring configuration of the substation, the operating modes include.

a) symmetrical monopolar mode of operation;

b) asymmetrical monopolar mode of operation;

c) earth return line mode of operation;

d) metal loop mode of operation.

4.2 Flexible DC system state

4.2.1 Maintenance state

The maintenance state of DC systems includes the following types.

a) Transformer maintenance. the transformer is under maintenance, the relevant grounding switch is closed (or the grounding wire is connected), and safety measures are in place.

b) Maintenance of converter valves, etc.. the starting resistor, grounding equipment, and converter valves are under maintenance; the metal return line changeover switch and disconnector, the earth return line changeover switch and disconnector, the DC pole (busbar) disconnector, the neutral line circuit breaker and disconnector are in the open state; the relevant grounding switch is in the closed state (or the grounding wire is connected), and safety measures are in place.

c) DC line maintenance. the DC pole (busbar) disconnector is in the open state, the pole line side grounding switch is in the closed state (or the grounding wire is connected), and safety measures are in place.

d) Grounding electrode line and grounding electrode maintenance. the circuit breaker and disconnecting switch of the grounding electrode line are in the open state, the grounding knife switch of the grounding electrode line is in the closed state (or the grounding wire is connected), and safety measures are in place.

4.2.2 Cold standby state

The cold standby state of a DC system includes the following types.

a) Converter cold standby. the AC incoming disconnect switch of the converter is in the open state; the metallic return disconnect switch, the earth return disconnect switch, the DC pole (busbar) disconnect switch, and the neutral circuit breaker are in the open state; the relevant grounding switch is in the open state; and the safety measures are removed.

b) DC line cold standby. the isolating switches of the DC poles (busbars) of the two substations are in the open state, the grounding switch on the pole line side is in the open state, and the safety measures are removed.

4.2.3 Polar isolation state

The DC field equipment is isolated from the DC line (including the grounding electrode line). The DC electrode (busbar) disconnecting switch, neutral line circuit breaker, metallic return line disconnecting switch, and earth return line disconnecting switch are in the open state.

4.2.4 Polar connection state

The DC pole (busbar) disconnector, neutral line circuit breaker, metallic return disconnector, and earth return disconnector are in the closed state.

4.2.5 Earth return line connection state

DC equipment is connected using the earth return line method.

4.2.6 Metal return line connection state

DC equipment is connected using the metal return line method.

4.2.7 Converter valve charging state

The converter valve is in a locked state, charging from either the DC or AC side.

4.2.8 Converter valve operating state

The converter valve is unlocked and put into operation.

5.1 Operation and management regulations

5.1.1 General management regulations

5.1.1.1 Personnel requirements

Operators must undergo job training and pass an examination before being allowed to work. They shall be familiar with the performance of primary equipment, secondary equipment, DC equipment, station power systems, auxiliary equipment, anti-mis- operation interlocking devices, fire protection equipment, and other equipment in the

VSC-HVDC substation (see Annex B for main equipment parameters), as well as the related lines and systems. They shall be proficient in using the system diagrams for primary, secondary, and auxiliary systems (see Annex C). They shall understand the jurisdiction of dispatching at all levels, dispatching terminology, and dispatching instructions.

5.1.1.2 Dispatch regulations

During normal switching operations and accident handling, operators must strictly follow instructions within the dispatching authority's jurisdiction. If operators have any questions about dispatching instructions, they shall promptly raise them with the dispatcher. Operations shall only proceed after confirmation that the instructions are correct.

5.1.1.3 Switching operation regulations

Operating personnel shall perform switching operations according to the instructions of the duty dispatcher or the person in charge of operations. The instructions shall be repeated to ensure accuracy before execution. Operators (including supervisors) shall understand the purpose and sequence of operations. If there are any questions about the instructions, they shall consult the issuer and execute only after confirming accuracy. A verification simulation shall be conducted before operation to ensure accuracy. The equipment name, number, and location shall be verified before operation. The supervisor's repetition system shall be strictly followed during operation. Operations shall be performed item by item in the order specified on the operation ticket. After each step, a checkmark "sqrt" shall be made after verification. A final check shall be performed after all operations are completed.

5.1.1.4 Equipment interlocking operation procedures

The following points shall be noted during equipment interlocking operations.

a) All high-voltage electrical equipment shall be equipped with comprehensive anti- mis-operation interlocking devices. Under normal circumstances, these devices shall not be taken out of service arbitrarily. Disabling anti-mis-operation interlocking devices requires approval from the equipment operation and maintenance management unit. Short-term removal of anti-mis-operation interlocking devices requires approval from the substation manager and must be recorded, and the devices shall be put back into service as soon as possible according to established procedures.

b) If an unlocking key is required for operation during equipment testing or acceptance, it must be done only after obtaining the consent of the authorized person, as per company regulations. During operation, the operating mode and equipment state of the DC system must be carefully verified to ensure that the operation shall not affect the operating equipment and system.

5.1.2 Protection setting management regulations

5.1.2.1 Protection setting retention

Protection setting sheets must undergo verification, approval, and stamping procedures.

Their setting management shall be carried out in accordance with relevant scheduling regulations.

5.1.2.2 Protection withdrawal

Equipment in operation must not operate without owner protection. The activation, deactivation, and modification of protection settings must be carried out according to dispatch commands. Appropriate safety measures must be implemented.

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