The level difference coordination principle of DC fuse and DC circuit breaker in DC power supply system is as follows:

1. All DC loads in substation must be equipped with DC protection appliances. According to the specific situation of the project, DC fuse is adopted, and even DC fuse and DC circuit breaker are mixed,

But attention should be paid to the cooperation between the superior and the subordinate. When the DC circuit breaker and DC fuse cooperate, the different action characteristics should be considered and the level difference should be adjusted appropriately.

The next level of DC circuit breaker should not be connected with DC fuse again.

2. If the upper and lower levels are DC circuit breakers, the rated current should be selected and matched according to the current level difference of level 4 or above;

3. If the battery outlet is a DC fuse and the lower level is a DC circuit breaker, the differential coordination should be selected according to 2 times or more of the rated current;

4. The number of DC protection devices in the substation should not exceed 4 levels;

When DC distribution panel is set in 5500kv substation, moulded case DC circuit breaker should be adopted for DC main feed panel;

The typical configuration scheme of DC circuit breaker and DC fuse of DC power supply system is recommended as follows:

1, The DC fuse with rated current of 315A can be used at the outlet of 1300ah battery, 400A DC fuse with rated current of 500ah battery, and 630A DC fuse with rated current of 630A can be used at outlet of 800ah battery.

2. The total output of 60A charging device can adopt the DC circuit breaker with rated current of 80A; the total output of 80A charging device can adopt the DC circuit breaker with rated current of 100A; the total output of 120a charging device can adopt the DC circuit breaker with rated current of 160A.

3. DC circuit breaker with rated current no more than 6A should be used for secondary equipment such as protection device, measurement and control device, fault recorder, PMU, safety automatic device and control circuit of circuit breaker.

Characteristic coordination of fuse and automatic air switch

When the expected short-circuit current is large and exceeds the rated breaking capacity of the automatic air switch, and the short-circuit current of the cargo system is too large, and there is no automatic air switch available, the combination mode of fuse and automatic air switch is adopted

It has the advantages of economy and simplicity.

1. The ampere second characteristic curve of fuse should be above the tripping curve of automatic air switch release, and keep enough distance. (Figure 1)

2. When the short circuit current of the system exceeds the rated breaking capacity of the automatic air switch, its curve shall be slightly less than the rated breaking capacity of the automatic air switch

The trip curves of instantaneous short-circuit release intersect to ensure that the automatic air switch trips when the short-circuit current is small,

When the short-circuit current exceeds the rated breaking capacity of the automatic air switch, it is broken by the fuse.

3. The rated current level of fuse shall be higher than that of automatic air switch to ensure the selectivity of breaking.

4. The fusing value of fuse shall not exceed the maximum allowable value of thermal overload release of automatic air switch.

In order to ensure the action selectivity between the automatic air switches, it must be required that the ampere second characteristics of the automatic air switches can cooperate safely and reasonably. The ampere second characteristic of automatic air switch is controlled by thermal release.

The thermal release is an inverse time characteristic, which is used as overload protection; the electromagnetic release is a transient characteristic, that is, when the current exceeds the given value, the power supply will be cut off instantaneously as the short-circuit protection (Fig. 2).

1) , in the overload protection zone

t1" > t2"

loth1/loth2>=kc1

Where: T1 "and T2" are the lower limit time and upper limit time of the thermal release characteristics of the first two automatic air switches respectively; loth1 and loth2 are the lower limit current of the thermal release of the first two automatic air switches at the same time respectively;

KC1: overload coordination coefficient of two-stage automatic air switch is related to the type and performance of circuit breaker, generally KC1 > = 2

(2) In short circuit protection zone

lot1/lot2>=kc2

Where: lot1 and LOT2 are the instantaneous tripping current of the last two-stage automatic air switch; kc2: the instantaneous tripping coordination coefficient of the two-stage automatic air switch,

It is related to the type and performance of circuit breaker, generally kc2 > = 1.5. In order to effectively realize the selective coordination of short circuit protection zone, different types of automatic air switches can be used for coordination.