FZN25-12DG Indoor High-Voltage Vacuum Load Break Switch Thomas Electric

Product Overview

The FZN25-12DG indoor high-voltage vacuum load break switch is a three-phase 50 Hz, 12 kV switching unit that combines the load break switch, the isolating switch and the earthing switch on one frame. It is built to GB 3804 for AC load break switches and GB 16926 for switch-fuse combination units, and serves as the incoming, sectionalizing and transformer-protection unit of 12 kV metal-enclosed and air-insulated switchgear. Two rated currents are offered, 630 A and 1250 A, both with 25 kA short-time withstand current and a spring energy-storage mechanism. In the FZRN25-12DG combination unit the circuit is completed with back-up fuses that clear short-circuit current, so the switch itself only makes and breaks load current.

Product Display

FZN25-12DG Indoor High-Voltage Vacuum Load Break Switch - display

FZN25-12DG Indoor High-Voltage Vacuum Load Break Switch - poster_display

Model Designation

FZN25-12DG Indoor High-Voltage Vacuum Load Break Switch - model

Model format: FZN25-12DG/T 630-25 or 1250-25 (load break switch) and FZRN25-12DG/T 200-31.5 (combination unit)

F: load break switch; Z: vacuum; N: indoor type
25: design sequence number; 12: rated voltage, kV
D: with earthing switch; G: with isolating switch; T: spring energy-storage mechanism
630 / 1250: rated current, A; 25: rated short-time withstand current, kA
R: combined with fuse; 200: rated current of the fuse, A; 31.5: rated short-circuit breaking current, kA
D and G are ordered separately when only one of the two switches is required; a 125 A fuse is available for lower-rated feeders

Service Conditions

Ambient temperature: +40 °C upper, -10 °C lower
Altitude: not more than 1000 m
Relative humidity: daily average not more than 95%, monthly average not more than 90%
Vapour pressure: daily average ≤ 2.2 × 10⁻³ MPa, monthly average ≤ 1.8 × 10⁻³ MPa
Seismic intensity: not more than 8 degrees
Site condition: indoor installation with no dripping, no fire or explosion hazard, no chemical corrosive gas and no violent vibration

Construction

The three poles are carried on a common metal frame, with the vacuum interrupters and the isolating and earthing switches supported on insulator bases and joined by flexible connections. Controls, position indication and the mechanism are grouped on the front operating panel, so all three switch positions can be operated and verified from the cubicle front.

In the combination unit the fuse is held between upper and lower clips and acts on the pole through a trip plate, so a blown fuse trips the switch and reports the loss of a phase. The isolating switch provides the maintenance break and the earthing switch bonds the de-energised side.

Technical Data

No.	Item	Unit	FZN25-12DG/T 630-25	FZN25-12DG/T 1250-25	FZRN25-12DG/T 200-31.5
1	Rated voltage	kV	12	12	12
2	Rated frequency	Hz	50	50	50
3	Rated current	A	630	1250	200 (fuse)
4	Rated short-time withstand current	kA	25	25	25
5	Rated peak withstand current	kA	63	63	63
6	Rated short-circuit making current	kA	63	63	—
7	Rated active load breaking current	A	1250	1250	1250
8	Rated closed-loop breaking current	A	1250	1250	1250
9	No-load transformer breaking capacity	kVA	2000	2000	2000
10	Earth fault current	A	20	20	20
11	Line and cable charging current under earth fault	A	20	20	20
12	Rated short-circuit breaking current	kA	—	—	31.5 or 50 (by fuse)
13	Rated transfer current	A	3150	3150	3150
14	Inherent opening time	ms	45	45	45
15	1 min power-frequency withstand voltage (phase and earth, vacuum gap / isolating gap)	kV	42/48	42/48	42/48
16	Lightning impulse withstand voltage (phase and earth, vacuum gap / isolating gap)	kV	75/85	75/85	75/85
17	Mechanical life	operations	> 10000	> 10000	> 10000

Selection note: the short-circuit breaking capability of the combination unit depends on the fuse fitted, 31.5 kA or 50 kA, and a 125 A fuse is available for lower-rated feeders. Coordinate the fuse with the 3150 A rated transfer current. Sites above 1000 m altitude and non-standard current or fuse combinations are subject to agreement between manufacturer and purchaser. Final parameters are subject to nameplate data and approved specifications.

Standards

The design follows GB 3804 for AC high-voltage load break switches (3.6 kV to 40.5 kV), GB 16926 for high-voltage load break switch-fuse combination units, and IEC 60265 and IEC 60420 for indoor switch-disconnectors and switch-fuse combinations.

Technical note: final parameters are subject to nameplate data and approved specifications.

Installation & Dimensions

Installation Diagram

FZN25-12DG Indoor High-Voltage Vacuum Load Break Switch - installation

The three-pole unit is bolted into the cubicle frame across an overall width of 886 mm, with a 650 mm mounting envelope, 600 mm between fixing centres, 210 mm phase spacing and an overall height of 997 mm. Charge the spring, confirm the closed, open and earthed positions on all three poles, verify the interlocking between load break switch, isolating switch and earthing switch, and on the combination unit fit the specified fuse between the upper and lower clips and confirm the trip plate engagement. Before energisation, carry out the 1 min power-frequency withstand test at 42 kV on the main circuit and 48 kV across the isolating gap, and bond the frame to the earth network of the switchgear.

Dimension	Value (mm)
Overall width	886
Mounting envelope	650
Fixing centres	600
Phase spacing	210
Overall height	997

Safety notice: installation, operation and maintenance must be performed by qualified professionals. Before maintenance, open the load break switch, then the isolating switch, close the earthing switch and verify absence of voltage. Do not use the load break switch to interrupt short-circuit current, and replace a blown fuse only with the same rated type.

FAQs

It is an indoor three-phase 12 kV vacuum switching unit that combines the load break switch, the isolating switch and the earthing switch on one frame, and serves as the incoming, sectionalizing and transformer-protection unit of 12 kV metal-enclosed and air-insulated switchgear. In service it makes and breaks rated load and closed-loop current up to 1250 A and switches no-load transformers up to 2000 kVA.

F is the load break switch, Z the vacuum medium, N indoor type, 25 the design sequence number, 12 the rated voltage in kV, D the earthing switch, G the isolating switch and T the spring energy-storage mechanism. The trailing figures give 1250 A rated current and 25 kA rated short-time withstand current. In the combination unit FZRN25-12DG/T 200-31.5, R marks the fuse, 200 the fuse rated current and 31.5 the short-circuit breaking current.

Both carry 25 kA short-time withstand current and a 63 kA peak, so the choice follows the feeder load rather than the fault duty. The 1250 A frame also sets the rated active load and closed-loop breaking current at 1250 A and the no-load transformer breaking capacity at 2000 kVA on both frames.

By the back-up fuses of the FZRN25-12DG combination unit, rated 31.5 kA or 50 kA depending on the fuse fitted, with a rated transfer current of 3150 A. The plain switch makes and breaks load current only and relies on upstream protection for faults; a 125 A fuse is available where the feeder demands a lower fuse rating.

The 1 min power-frequency withstand voltage is 42 kV phase-to-earth and across the vacuum gap and 48 kV across the isolating gap, with 75/85 kV lightning impulse on the same arrangement. Mechanical life exceeds 10000 operations and the inherent opening time is 45 ms.

The D and G suffixes add the earthing switch and the isolating switch and are ordered separately when only one of the two is required. Order both where the unit is the visible break point of the panel, so the maintenance break and the maintained earth are both available at the cubicle front.

FZN25-12DG Indoor High-Voltage Vacuum Load Break Switch