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Home » Products » Pole Mounted Switch » FZW28-12(F) Load Switch (Watchdog)
FZW28-12(F)

Load Switch (Watchdog)

The FZW28-12(F) load switch is also called watchdog. The users of 10kV overhead power distribution line through a T connection can cause the protective trip of the outgoing line switch in a transformer substation. Such problems happen when 1) faults occur at users’ incoming line, 2) or the protective motion time does not match that of the outgoing line switch of the substation, even though faults occur at the incoming line switch on user’s side.

If, unfortunately, the faults are permanent, then the substation can not be reconnected. Thus the accidents happened at the client’s end will paralyze the whole distribution line, causing serious society impacts.

However, our FZW28-12(F) load switch can avoid these accidents effectively. Installed at the responsibility demarcation point on the 10kV overhead distribution line, the watchdog can automatically disconnect the lines with single phase earthing fault or short circuit fault between phases, ensuring the safety of the power supply for normal clients.

Typical function
1. Automatically disconnecting single phase earthing line.
When a single phase earthing problem happened to a branch, the FZW28-12(F) load switch at the demarcation point will automatically disconnect the fault line, ensuring the normal power supply for users on the other braches of the feeder line, and the safe operation of the substation.

2. Automatically isolating the fault line with short circuit between phases.
When there is a short circuit problem at a branch line, the FZW28-12(F) load switch at the demarcation point will disconnect the fault line immediately after the trip of the outgoing line of substation. Then after the outgoing line of the substation is reconnected, the fault line will be isolated, while power supply for users on the other branches of the feeder line will be recovered.

3. Fast positioning of the fault line.
After the disconnection, the power supply for responsible users will be cut off. They can report the fault information to the electric power company, so the fault can be positioned and resolved soon.

4. Monitoring users’ load.
The FZW28-12(F) load switch at the demarcation point can transfer the monitoring data to the power control center for real-time monitoring of the load far away.

Solution for the watchdog’s faults
The technical parameters of the controller
NO. Item Data
1 Rated voltage 12kV
2 Gap insulating level Power frequency withstand voltage (dry test/wet test, phase to phase and phase to earth, across open contacts) 48kV
Lighting pulse peak testing voltage 85kV
3 To earth and phase to phase insulating level Power frequency withstand voltage (phase to phase and phase to earth) 42kV
Lightning impulse test peak voltage 75kV
4 Rated current 630A
5 Rated thermal stable current 16kA
6 Rated thermal stable time 2S
7 Rated short circuit peak making current 40kA
8 Rated peak withstand current 40kA
9 Rated cable charging breaking current 20A
10 Rated switching no-load transformer inductor current <5A
11 Closing time (built-in isolator motion time included) 120ms ~180ms
12 Opening time 15ms ~40ms
13 Mechanism endurance 10000time
14 Interlock current setting value range <6ms
15 Opening / closing synchronism <5ms
16 Loop circuit resistance <700 μΩ
17 Rated SF6 pressure 0.002MPa
The technical parameters of the controller
NO. Item Data Note
1 Input working voltage AC220V ±20%  
2 Input working frequency 50Hz  
3 Overall power consumption <10W  
4 Output voltage (opening operation) DC48V  
5 Output control contact rating DC48V, 8A  
6 Output power (opening operation) DC48V, 8A  
7 sampling phase voltage input value 0~264V  
8 sampling phase current input value 0~20A 5A or higher saturation current allowed
9 sampling zero sequence current input value 0 ~20A 5A or higher saturation current allowed
10 Phase to phase protective movement setting range 0.5A ~5A 20 grades (step length: 0.25A)
11 Phase to phase protective movement delay time 0.3S Adjustable by software
12 Zero sequence protection current setting range 10mA ~200mA 20 grades (step length: 10mA)
13 Zero sequence protective movement delay time 0 ~2S 5 grades (step length: 0.5S)
14 latching current setting value range 6A Adjustable by software
15 Low voltage latching setting value range 66V Adjustable by software
16 Setting value error allowance ±5%  
Shape dimension and installation dimension
Shape dimension of the switch

1. Close the circuit for energy storage
2. Manual closing lever
3. Opening and closing knob
4. Power

Installation dimension on the pole

1.(rocket) Fastener
2. Cross arm
3. Utility pole
4. (rocket) Fastener
5. (rocket) Fastener
6. Demarcation switch
7. Demarcation switch controller

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