Grid companies' technical requirements for inverter access to distribution networks

Distributed power sources of 10 kV and below are divided into two types according to the form of access to the grid: inverters and rotating motors. Inverter type Distributed power sources are connected to the grid through inverters, mainly including photovoltaics, full-power inverter grid-connected wind turbines, etc.

Technical requirements for inverter-type distributed generation connected to 10 kV distribution network

1. The grid connection point should be equipped with a disconnecting device that is easy to operate, lockable, has obvious disconnecting points, has a grounding function, and can interrupt fault currents.

2. The inverter should comply with relevant national and industry technical standards, and have high/low voltage lockout and automatic grid-connection when voltage is detected (see Table 1 for voltage protection action time requirements; automatic grid-connection when voltage is detected at 85% UN).

Table 1: Voltage protection action time requirements

3. When the distributed power source is connected via a dedicated line, the dedicated line may not have a reclosing switch or may disable it.

4. When the public power grid line is put into automatic reclosing, it is advisable to add the reclosing no-pressure detection function; if the conditions are not met, it should be checked whether the reclosing time is coordinated with the distributed power supply connection and disconnection control time (the reclosing time should be set to 2+ δt seconds, δt is the protection coordination difference time).

5. The power factor of distributed power supply should be adjustable within the range of 0.95 (leading) to 0.95 (lagging).

Technical requirements for inverter type distributed power supply connected to 220/380V distribution network

1. The grid connection point should be installed with a low-voltage grid-connected special switch that is easy to operate, has obvious opening and closing indications, and has the ability to break fault current. The special switch should have the functions of under-voltage tripping and under-voltage detection closing. The under-voltage tripping setting should be set to 20%UN and 10 seconds, and the under-voltage detection setting should be set to greater than 85%UN.

2. The inverter should comply with relevant national and industry technical standards, and have high/low voltage lockout and automatic grid-connection when voltage is detected (see Table 1 for voltage protection action time, automatic grid-connection when voltage is detected at 85% UN).

3. When the access capacity of distributed power generation exceeds 25% of the rated capacity of the distribution transformer in this substation, the knife-fused main switch on the low-voltage side of the distribution transformer should be transformed into a low-voltage main switch, and an anti-islanding device should be installed at the low-voltage bus of the distribution transformer; the low-voltage main switch should have an operational locking function with the anti-islanding device, and when there is communication between the busbars, the connecting switch should also have an operational locking function with the anti-islanding device.

4. When the distributed power source is connected to the 380V distribution network, a three-phase inverter should be used; before the distributed power source is connected to the 220V distribution network, the total capacity of single-phase access in the same area should be checked to prevent three-phase power imbalance.

5. The power factor of distributed power supply should be adjustable within the range of 0.95 (leading) to 0.95 (lagging).

This article is excerpted from the State Grid's "Technical Specifications for Distributed Generation Access to Distribution Networks (Revised Edition)"