ZBZ-1 type rotor two-point grounding protection deviceDetailed product description：

The ZBZ-1 rotor two-point grounding device is suitable for protecting the DC magnetic circuit (rotor circuit) two-point grounding of synchronous generators.
2. Structure and action principles
The principle wiring is shown in Figure 1, mainly composed of ZBZ-1 type grounding (electromagnetic instantaneous action) relay 5 (internal wiring shown in Figure 2), FY-1 type anti current coil 6 and FY-1/B inverter 7, etc. The other components in Figure 1 are configured during screen assembly to illustrate their working principle.
When a grounding fault occurs in the excitation circuit of the generator, it does not constitute a fault current circuit and does not immediately pose a threat to the operation of the generator. While taking countermeasures, it can still continue to operate. If a two-point grounding fault occurs, it is not the case, and some excitation coils may be short circuited, even causing a fire. Therefore, after a grounding occurs in the excitation circuit of the motor, two-point grounding protection should be immediately activated.
The protection device is constructed using the principle of DC bridge balance.
Connect voltage divider 1 to the lead wire of the generator excitation coil slip ring, and the device is located between the sliding contact of 1 and the ground. When the excitation coil generates a grounding point (set as D1), a four arm bridge is formed with the sliding contact of voltage divider 1 and the grounding point as the diagonal. According to the principle of bridge balance, the resistance relationship between the four arms is R1 · R4=R2 · R3. Therefore, when a grounding occurs in the excitation circuit (during the measurement of the insulation resistance of the excitation circuit to ground), the protection device should be immediately put into operation, that is, close S, disconnect connection piece 2, close button 3, adjust the sliding contact of voltage divider 1, change its resistance values on both sides, set R3 and R4, until millivolt meter 4 indicates zero, at which point the "bridge" is in a balanced state. There is no current in coil I of instantaneous relay 5. Then open button 3 and connect connector 2. Place the device in a ready state.
When there is another grounding point in the excitation circuit, set the grounding point to D2, and it becomes a two-point grounding fault. As shown in Figure 1, the excitation coil between D1 and D2 is short circuited, the impedance of one arm decreases, the "bridge" loses balance, and current flows through the relay and coil. If the current is greater than the operating current of relay 5, the protection device will activate and cut off the generator.

Due to the uneven air gap between the generator rotor and stator magnets, the magnetic flux in various parts of the excitation coil will fluctuate due to the rotation of the rotor, and pulsating AC potential will be induced in the excitation coil with the increase or decrease of the air gap. Therefore, after the protective device is put into operation, AC current will be generated in coil 1 of relay 5. If the current is greater than the operating current of relay 5, the protection device will malfunction. In order to reduce the impact of this AC current on the protection device, an anti current coil "6" is connected in series with the coil I of relay "5" on the diagonal of the "bridge", and a compensation current transformer "7" that changes to 1 is used. The primary winding of the current transformer is connected in series with the relay coil I, and the secondary winding is connected to coil II of "5". When the AC current passes through the diagonal of the "bridge", the magnetic flux generated by the secondary circuit of the transformer is opposite in direction and equal in value to the AC magnetic flux component generated in coil I, thus greatly reducing the sensitivity of the relay under AC current. Due to the small DC resistance of the primary winding of the anti current coil and compensating current transformer, the transformer cannot transmit DC current, and their impact on the DC current during faults is also minimal.
The internal wiring diagram of relay 5 is shown in Figure 2, and the external appearance and installation dimensions can be found in the HK-01 housing in the appendix of this manual,
The accessory anti current coil and inverter have no base or shell, and can be directly installed behind the screen board of the enemy detection relay. Their appearance and installation hole size are shown in Figure 3.

3. The technical data of ZBZ-1 rotor two-point grounding protection device is shown in Table 1

Model Name	Technical data	Qualitative classification intensity	structure
ZBZ-1 relay	Action current: DC70 ± mA, each coil Return coefficient: ≥ 0.5 Action time: 0.25s, at 1.2 times the action current Contact capacity: DC ≤ 250V, ≤ 0.5A, τ=0.5 ± 0.75,50W AC 250VA	50Hz 2kV 1min	adopt HK－01a HK－01b
FY-1/K anti current coil	DC resistance: 8.5 Ω Impedance: 5k Ω, when f=50Hz and 1=0.04A
FY-1/B inverter	Transformation ratio: 1 Error: ± 3%, when the current does not exceed 0.2A