ZW8‑12
Pole Mounted Outdoor Vacuum Circuit Breaker

Technical Specifications

The ZW8‑12 is built on one tank and one frame across the whole rating range. What changes between ratings is the interrupter, the contact assembly and the mechanism spring.

Values above describe the standard ZW8‑12 platform and are given as typical ratings. The rating combination of a specific breaker follows the approved drawing, the interrupter fitted and the mechanism ordered. The sealed IP65 variant, the 1250 A rating and ratings with an integral isolating switch are quoted on application.

Service Conditions

The ZW8‑12 is mounted on a pole in the open. It has no kiosk and no canopy, so the site conditions below are part of the specification rather than a general note.

Sites outside these limits — high altitude, heavier ice loading, a lower minimum temperature or a different pollution class — are handled by agreement at the enquiry stage, because the external insulation, the tank sealing and the mechanism heater are selected against them.

Construction & Operating Principle

Three-phase common tank

The three vacuum interrupters are housed in a single steel tank rather than in three separate columns. Phase-to-phase and phase-to-earth insulation inside the tank is provided by solid SMC insulating material, so the tank stays small and light and the breaker is easier to lift onto the pole than a three-column design of the same rating. The primary terminals are brought out through bushings on the tank walls.

Sealed, condensation-controlled enclosure

The tank is sealed against rain and dust, and a breather with a silica gel desiccant in the base keeps the internal air dry so that condensation does not form on the interrupters when the temperature drops overnight. The desiccant is the one consumable on the breaker: it is inspected at the periodic check and replaced when its colour turns light yellow. A fully sealed stainless tank rated IP65 is available for coastal, desert and heavily polluted sites.

Operating mechanism

The mechanism is a CT23 spring stored-energy type, mounted in a sealed box below the tank. It can be charged by hand or by a motor, and it opens and closes all three poles together. The closing spring is recharged automatically after each closing operation, and manual opening and closing are available for commissioning with the control supply removed. The open / close indicator is visible from ground level.

Combined breaker with isolating switch

The ZW8‑12G is the same breaker with an isolating switch bolted to the frame. The isolating switch gives a visible break in the line — the property that makes it usable as a sectioning point — and it is mechanically interlocked with the breaker so that the switch cannot be opened while the breaker is closed.

Models, Current Transformers & Automation

Model versions

The ZW8‑12 is supplied in four arrangements. The basic ZW8‑12/T is a plain pole‑mounted breaker with the CT23 spring mechanism. The ZW8‑12G adds an integral isolating switch with a visible break. The /PT version carries a voltage transformer on the frame for a local control supply. The ZW8‑12F and /FG are the intelligent versions described below.

Current and voltage transformers

Two or three current transformers can be fitted inside the tank, one per phase, and a dual-winding transformer can serve both metering and protection so that a revenue meter and a protection relay can be fed from the same unit. Typical ratios are 200/5, 400/5 and 600/5 A, selected to the line loading. Fitting the transformers inside the tank removes the separate CT pedestal and the extra primary connections that go with it. A voltage transformer, where fitted, is mounted on the frame and supplies the control and automation equipment.

Automation and remote control

With a controller mounted on the frame, the ZW8‑12F works as a recloser or a sectionaliser rather than as a plain breaker. The breaker then supports remote measurement, remote signalling, remote control and remote adjustment through the controller's communication port, and it can reclose automatically after a transient fault. Automatic sectioning also lets the healthy part of a line be restored without sending a crew to the fault.

Combined controller function

Where inrush current is a problem — typically on a line feeding transformers energised together — a combined controller is fitted to suppress the closing inrush. This is a common requirement on rural networks where several distribution transformers are switched at the same point on the feeder.

Available Ratings & Options

Four arrangements cover almost every requirement on a 12 kV overhead line. Because the tank and frame are common, the choice is mainly about the switching duty and whether a visible break or remote control is needed.

The rating and the option set are quoted together. Because the transformer ratios and the controller interface are project items, the enclosure and the frame drawing are issued with the offer.

Key Features

Applications

The ZW8‑12 is used wherever a 12 kV overhead line has to be switched, sectioned or protected in the open — on the line itself, at a pole substation, or at the incoming point of a plant.

What We Need to Quote Your Breaker

The breaker is configured to the line and to the pole, so the enquiry has to carry the electrical duty, the automation requirement and the mounting arrangement. With the items below we can return a firm quotation and a frame drawing.

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

Standards & Documentation

Type test reports for the ZW8‑12 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. Tank assembly, interrupter fitting, wiring and routine testing all happen in‑house, which keeps both the delivery schedule and the quality check inside our control.