Overview

The ZN28-12 series indoor high-voltage vacuum circuit breaker is a three-phase AC 50Hz device with a rated voltage of 12kV, designed for compliance with GB1984-89 standards. It is available in two installation forms: an integrated structure (ZN28-12) combining the circuit breaker and operating mechanism, and a separated structure (ZN28A-12) for use with fixed switchgear such as GG-1A(Z) and XGN2A10(Z). The breaker supports various operating mechanisms, including CD17/CD10A DC electromagnetic types and CT17/CT19 spring energy storage types, making it suitable for diverse and reliable indoor high-voltage applications.

Type Designation of  ZN28-12KV

• Z: Vacuum circuit breaker.
• N: Indoor type.
• 28: Design sequence number.
• 12: Rated voltage (kV).
• A: Separation structure. B: One-piece structure.
• □: Rated current (A).
• □: Rated short-circuit breaking current (kA).

Structural Features of Vacuum Circuit Breake

The ZN28-12 series vacuum circuit breaker is specifically designed for use in fixed switchgear cabinets. It is equipped with a self-contained operating mechanism, offering flexibility for users to choose between the CT-19 spring energy storage mechanism or the CD-17 electromagnetic mechanism based on their specific requirements. The operating mechanism is integrated within the frame and connected to the main shaft via a connecting rod, ensuring a precise spindle rotation angle of 58° ± 1°. The mechanical performance and technical parameters comply with the specifications outlined in the technical table.

The circuit breaker features a sealed longitudinal magnetic field vacuum arc extinguishing chamber for efficient arc interruption. Key components such as the main shaft, opening spring, and oil buffer are securely housed within the frame, which includes pre-drilled mounting holes on its base for easy installation. On the rear of the frame, six insulators (three upper and three lower) are installed:

• Upper insulators: Secure the moving bracket.
• Lower insulators: Secure the static bracket.

The rear ends of the moving and static brackets double as outlet terminals. The vacuum interrupter is mounted between the dynamic and static brackets and is connected to the main shaft via an insulating rod and swing arm. Two additional insulating rods are installed between the brackets to form a unified structure, enhancing the overall strength and stability of the breaker.

Service Conditions for ZN28-12 Indoor High-Voltage Vacuum Circuit Breake

1. Ambient Temperature: -10℃ to +40℃.
2. Altitude: ≤1000m.
3. Humidity:
   • Daily relative humidity ≤95%.
   • Monthly relative humidity ≤90%.
   • Daily water vapor pressure ≤2.2kPa, monthly ≤1.8kPa.
4. Air Quality: Free from dust, smoke, corrosive or combustible gases, vapors, or salt spray.
5. Vibration: Minimal external vibrations or ground motion.
6. Electromagnetic Interference: Induced voltage in the secondary system ≤1.6kV.

Technical Parameters of ZN28-12 Vacuum Circuit Breaker

Item				Unit	20kA	25kA	31.5kA	40kA
Rated Voltage				kV	12
Rated Current				A	630 1000 1250	1250 1600	1250,1600 2000,2500	1600 2500 3150
Rated Short-Circuit Breaking Current				kA	20	25	31.5	40
Rated Short-Circuit Closing Current (Peak)				kA	50	63	80	100
Rated Peak Withstand Current				kA	50	63	80	100
4s Rated Short-Time Withstand Current				kA	20	25	31.5	40
Rated Insulation Level	Power Frequency Withstand Voltage (After Breaking)			kV	42 (Break 48)
	Impulse Withstand Voltage (After Breaking)			kV	75 (Break 85)
Rated Operating Sequence					Open–0.3s–Close Open–180s–Close
Mechanical Life				Times	10,000
Rated Short-Circuit Current Breaking Times				Times	30	30	30	20
Operating Mechanism Voltage		Rated Operating Voltage		V	110, 220	110, 220	220	220
		Rated Closing Current		A	71	71	71	128
		Rated Opening Voltage		V	AC/DC 110, 220
		Rated Opening Current		A	3.0
Contact Opening Distance				mm	11 ± 1
Overtravel (Contact Spring Compression Length)				mm	4 ± 1
Three-Phase Closing Non-Synchronism				ms	≤2
Contact Closing Bounce Time				ms	≤2
Average Opening Speed (Pole 6mm)				m/s	1.2 ± 0.3
Average Closing Speed				m/s	0.6 ± 0.2
Opening Time			Maximum Operating Voltage	s	≤0.06
			Minimum Operating Voltage	s	≤0.08
Closing Time				s	≤0.1
Main Circuit Resistance				μΩ	≤50
Cumulative Contact Wear Allowance				mm	3
Oil Buffer Stroke				mm	10

Outline and installation dimensions

Figure 1: ZN28-12 Vacuum Circuit Breaker Outline Diagram (Basic Model)

Item	20kA	25kA	31.5kA	40kA
a	230			275 ± 1
b	600			690
c	707			842
d	560			652
e	293-20			342-20
f	227 ± 1			227 ± 1

Figure 2: ZN28A-12 Vacuum Circuit Breaker Outline Dimensions

Rated Current	20kA, 25A, 31.5kA	40kA
Dimension (a)	250	275
Dimension (b)	610	690

Figure 3: ZN28A-12 Vacuum Circuit Breaker Primary Connection Dimensions for 20~31.5kA

FAQs for ZN28-12 Vacuum Circuit Breaker

1. What applications is the ZN28-12 vacuum circuit breaker designed for?
   It is ideal for 12kV power systems in industrial facilities, mining enterprises, power plants, and substations requiring reliable fault protection and frequent switching.
2. What installation options are available for the ZN28-12 circuit breaker?
   The breaker is available in integrated and separated structures, with options for fixed installation or use in switchgear cabinets like GG-1A(Z) and XGN2A10(Z).
3. What is the mechanical lifespan of the ZN28-12 breaker?
   The breaker is rated for up to 10,000 mechanical operations, making it suitable for demanding operational conditions.
4. How does the ZN28-12 ensure efficient arc extinguishing?
   It uses a longitudinal magnetic field vacuum arc extinguishing chamber, providing rapid and reliable fault clearance.
5. What are the insulation capabilities of the ZN28-12?
   It has a power frequency withstand voltage rating of 48kV and an impulse withstand voltage rating of 85kV, ensuring safety in high-voltage environments.
6. Is the ZN28-12 customizable for unique project requirements?
   Yes, the breaker offers customization options, including rated current, short-circuit breaking capacity, and operating mechanisms. Contact the technical team for tailored solutions.

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