ZW32 Series
Outdoor Vacuum Circuit Breaker, 10 kV to 40.5 kV

Technical Specifications

The table below puts the three voltage classes side by side, because that is how a ZW32 is actually chosen: the system voltage fixes the class, and the class fixes the insulation levels, the phase spacing and the contact travel. Everything else – current rating, breaking capacity, current transformers, isolator, controller – is selected inside the class. Where a value differs with the configuration ordered, the full range is given and the figure that applies is confirmed on the approved drawing.

Values above describe the standard ZW32 platform and are given as typical ratings. The rating combination of a specific breaker follows the approved drawing, the current transformers fitted and the operating mechanism ordered. Operation at 60 Hz, other control voltages, a higher current rating inside a class, heavier pollution, higher altitude and an integral isolating switch are all quoted on application. The weights exclude the pole‑top frame and the controller.

Reading The Model Code

A ZW32 is ordered by its designation, so the designation is worth reading as three separate decisions: the voltage class, the current and breaking rating, and the options.

A typical order therefore reads ZW32‑24/T1250‑25/G: 24 kV class, spring mechanism, 1250 A, 25 kA, with an integral isolating function. Because the designation carries the rating, it is the string we quote against and the string that is stamped on the nameplate.

Service Conditions

The ZW32 stands on an outdoor frame with its insulators exposed, so the external insulation is sized against the pollution level and the altitude rather than against the interrupting duty. The envelope below applies to all three voltage classes.

Sites outside these limits — high altitude, a lower minimum temperature, heavier ice loading or a different pollution class — are handled by agreement at the enquiry stage, because the creepage distance of the columns, the phase spacing and the mechanism heater are all selected against them. The 12 kV class is routinely built for altitudes up to 2000 m; above 1000 m the 24 kV and 40.5 kV classes are re-rated for the reduced dielectric strength of air.

Available Voltage Classes

The same column construction, the same spring mechanism and the same frame drawing are used across the three classes, so the spare-parts list and the operating procedure stay the same as a network grows from 10 kV to 35 kV. What changes between the classes is the insulation level, the phase spacing and the contact travel.

Transformer ratios, the controller interface and the mounting frame are project items. The column arrangement, the outline drawing and the secondary circuit diagram are issued with the offer once the transformer ratios are fixed.

Construction & Operating Principle

The three classes share one mechanical architecture, so the description below applies to a ZW32 whatever its class; the figures that change with the class are the phase spacing and the contact travel given in the table above.

Three separate interrupter columns

Each phase is built as an independent column: a vacuum interrupter held inside a solid‑insulated cylinder, with the incoming and outgoing terminals brought out at the top and the bottom of the same column. The three columns stand on a common steel frame at a fixed phase spacing – about 340 mm in the 12 kV class, 380 mm in the 24 kV class and about 460 mm in the 40.5 kV class. Keeping the phases in separate columns rather than in one tank raises the dielectric clearance available between phases and lets the interrupter assembly be larger, which is how the ZW32 reaches its breaking capability at each voltage.

Solid insulation, no oil and no gas

The interrupter is enclosed in a cast epoxy cylinder produced by vacuum casting, with the external sheds either cast into the same part or covered with a silicone rubber housing for coastal and heavily polluted sites. The interrupter itself breaks in vacuum. There is no oil to test or replace and no insulating gas to monitor or top up, so the only routine work on the breaker is a visual check and an operating test.

Drive linkage and spring mechanism

The three insulating pull rods are driven from a common shaft through a linkage, so the three poles open and close together inside the asynchronism limit. The spring mechanism, housed in a sealed box on the frame, stores the closing energy; it is charged by the energy-storage motor and, for commissioning or where the control supply is not available, by hand. Opening is driven by the opening spring in the mechanism, and a manual emergency opening device is fitted as standard.

Optional isolating function

The ZW32 can be supplied with an isolating function so that the unit also provides a visible break. The column arrangement is then extended so that the open position gives an isolating distance that satisfies the across-the-gap withstand values in the table above, and the mechanism indicates the position. The feature is identified in the type designation and is mechanically interlocked with the breaker position, so it cannot be operated with the breaker closed. Surge arresters can be mounted on the same frame.

Current Transformers, Isolating Function & Automation

Built-in current transformers

Two or three current transformers can be fitted on the breaker, one per phase, mounted around the primary connection at the top of each interrupter column. Typical ratios are 200/5, 400/5 and 600/5 A, selected to the line loading, and a dual-winding transformer can serve metering and protection from the same unit. Because the transformer is carried by the column, the separate CT pedestal with its own primary connections and its own earthing disappears from the pole. Zero-sequence transformers and voltage sensors can be added alongside for an earth-fault and voltage-measurement scheme.

Isolating switch and interlock

Where a visible break is required, an isolating switch is added as a separate blade assembly on the same frame rather than by combining it with the interrupter. The switch is mechanically interlocked with the breaker so that it cannot be operated while the breaker is closed, and the interlock holds with the control supply removed.

Automation and remote control

With a controller mounted on the frame, the ZW32 works as an automated sectioning or reclosing point. Remote measurement, remote signalling, remote control and remote adjustment are carried over the controller communication port, so the utility can see and operate the switch from the control centre. Closing back onto a transient fault and isolating a faulted span are both supported. The same controller is used across all three voltage classes, so an operator who knows the 12 kV installation already knows the 40.5 kV one.

Application as a boundary switch

At the demarcation point between a utility network and a customer installation, the breaker with a controller acts as the boundary switch: it isolates the customer fault from the utility feeder and reports it, so a fault inside the customer installation does not take out the whole line. This is one of the most common duties for a pole-mounted vacuum breaker at any of the three voltage classes.

Selecting A ZW32 For Your Network

The three classes overlap in current and in breaking rating, so the choice is made on the system voltage and on what the network has to do, not on the physical size of the breaker.

10 kV systems — the 12 kV class

This is the standard answer for a 10 kV overhead network, and it is also the class in which the widest range of ratings is available. One platform covers line switching, transformer incomer protection, boundary metering and automated sectioning; specify 20 kA unless the utility fault-level calculation says otherwise, and 25 kA where the network is stiff or is being reinforced.

20 kV systems — the 24 kV class

Specified when a 10 kV network is uprated to carry more load over the same right of way, and on networks that were built at 20 kV from the start. The phase spacing widens to 380 mm and the interrupter assembly is larger, which is what the higher system short-circuit level of a 20 kV network requires. Current transformers, the isolator and the controller are the same items as in the 12 kV class.

35 kV systems — the 40.5 kV class

The same compact construction carried up to 40.5 kV, instead of the porcelain-column arrangement conventionally used at this level. It is supplied from 630 A to 1600 A with breaking capacity to 31.5 kA, and its weight and footprint make pole and platform mounting practical where a porcelain-column breaker would need a substantially heavier structure.

Confirming the class before quoting

If the class is not yet fixed, send the system voltage, the maximum and minimum load current and the fault level at the point of installation. We will confirm the class, the current rating and the breaking capacity, and state which of the two applies before a price is put on the enquiry.

Key Features

Applications

The ZW32 is used wherever a 10 kV, 20 kV or 35 kV network has to be switched outdoors — on the overhead line, at a pole substation, or at the incoming point of an industrial installation.

What We Need to Quote Your Breaker

The breaker is configured to the line, the pole and the automation requirement. With the items below we can return a firm quotation, the frame drawing and the controller interface list.

Send these to gohointl@gmail.com and we will reply with a priced offer, the outline drawing for the pole or platform frame, the secondary circuit diagram and the routine test plan for the breaker.

Standards & Documentation

Type test reports for the ZW32 platform and the routine test record for the individual breaker are available for project qualification on request.

Breakers are assembled in our own factory in Yueqing, Zhejiang — the same site that builds our switchgear, transformers and prefabricated substations. Column casting, interrupter fitting, linkage alignment, wiring and routine testing all happen in‑house, which keeps both the delivery schedule and the quality check inside our control.