LW38-252

Self-blast SF6 circuit breaker

Three-phase outdoor SF6 circuit breaker for 252 kV, 50 Hz substations and transmission lines. It makes and breaks rated and short-circuit currents and supports fast auto-reclosing.

Key parameters

Rated voltage: 252 kV
Rated current: 4000 A
Rated short-circuit breaking current: 40 kA
Rated operating sequence: O – 0.3 s – CO – 180 s – CO
Mechanical endurance: 5,000 operations

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General information

LW38-252 is a three-phase self-blast SF6 circuit breaker for outdoor installation in 50 Hz high-voltage AC networks, at substations and on transmission lines. It is designed to make and break rated currents and short-circuit currents, as well as to switch lines, providing protection, control and switching operations in power transmission and transformation systems. It supports opening, closing and fast auto-reclosing, as well as three-pole electrically ganged operation.

The circuit breaker is built on the latest design principles: simple construction, compact dimensions, low material consumption, low required operating energy, high reliability, easy installation and low noise. It is a new generation of high-voltage SF6 circuit breakers.

Service conditions

Ambient temperature: −40 °C … +50 °C.
Wind pressure: not more than 700 Pa.
Altitude: not more than 3000 m.
Seismic intensity: not more than 9 degrees.
Air pollution level: III.

Ratings of the circuit breaker and operating mechanism

Table 1

Parameter		Unit	Value
Rated voltage		kV	252
Rated insulation level		kV	see Table 2
Rated frequency		Hz	50
Rated current		A	4000
Rated short-circuit breaking current		kA	40
Rated short-time withstand current		kA	40
Rated peak withstand current		kA	100
Rated duration of short circuit		s	3
Rated short-circuit making current (peak)		kA	100
Rated short-line fault breaking current		kA	30/36
Rated line-charging breaking current		A	125
Rated out-of-phase breaking current		kA	10
Total number of rated short-circuit current breaking operations		operations	20
First-pole-to-clear factor			1.3
SF6 pressure (at 20 °C)		MPa	see Table 3
Rated supply voltage of control and auxiliary circuits			see Table 5
Rated operating sequence			O – 0.3 s – CO – 180 s – CO
Mechanical characteristics			see Table 4
Main circuit resistance		µΩ	50
Mechanical endurance of the circuit breaker		operations	5000
Static terminal load	Horizontal longitudinal F_shA	N	1500
	Horizontal transverse F_shB	N	1000
	Vertical F_tVm	N	1250
Annual SF6 leakage rate			≤ 1 %
SF6 moisture content (×10⁻⁶)		by volume (V/V)	≤ 150
Contact stroke		mm	200 (+4 / −4)
Contact engagement (overtravel)		mm	28 (+4 / −2)

Table 2. Insulation level

Parameter		Value, kV
1 min power-frequency withstand voltage (r.m.s., dry and wet test)	Across the isolating distance	460+145
	Between poles, to earth	460
Lightning impulse withstand voltage (peak, full wave 1.2/50 µs)	Across the isolating distance	1050+200
	Between poles, to earth	1050
5 min power-frequency withstand voltage (r.m.s.) at zero SF6 gauge pressure	Across the isolating distance	220
	Between poles, to earth	220

Table 3. SF6 pressure (at 20 °C)

Parameter	Value, MPa
Rated filling pressure P_rm	0.4 ± 0.015
Refilling alarm pressure P_am	0.35 ± 0.015
Minimum functional pressure P_me	0.32 ± 0.015
P_am − P_me	0.018 … 0.022
Gas filling pressure for packing and transport	0.025

Table 4. Mechanical characteristics

Parameter	Unit	Value
Opening time (upper and lower limits)	ms	≤ 34
Closing time (upper and lower limits)	ms	100
Open–close time (O–C)	ms	factory tests ≤ 300, in service ≥ 300
Close–open time (C–O)	ms	factory tests ≤ 60, in service ≥ 60
Pole non-simultaneity on opening	ms	≤ 3
Pole non-simultaneity on closing	ms	≤ 5
Break time	ms	60
Opening speed	m/s	7.0–7.5
Closing speed	m/s	2.8–3.8

Table 5. Rated supply voltage of control and auxiliary circuits

Parameter	Unit	Value
Control and signalling circuit voltage	V	DC 220
Rated motor voltage	V	DC 220
Anti-condensation heater circuit voltage	V	AC 220

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