CZ Vacuum Type on-Load Tap Changer for Dry Type Transformers

General

The CZ type vacuum on-load tap changer (abbreviated as OLTC), suitable for dry type transformer installed

indoor, serves for voltage ratio adjustment under load of dry type transformer by realizing tap changes without

interruption. The CZ on-load tap changer, designed in single-phase structure,can be applied on any

transformer winding connections (star, delta, etc.). For dry type three-phase transformer, three sets of single-

phase CZ OLTC can be mechanically coupled and operated by one unit of motor drive unit (abbreviated as

MDU). CZ OLTC consists of diverter switch which executes high-speed resistor transition and tap selector. At

first, the tap terminal is selected via tap selector and the subsequent switch under load is carried out through

diverter switch. Vacuum interrupters serve as arc contacts of diverter switch while the load of main circuit is

carried by specific main contact set.

For any standard CZ equipment delivery, one unit of MDU is comprised to achieve mechanical operation of

OLTC (please refer to operation instructions of MDU for its running principles). It can function for local and

remote control modes and is able to be installed outdoor due to its protective housing. In case of CZ OLTC

equipped with huge cabinet, the MDU can be mounted on side surface of the cabinet.

Main characteristics

1 Vacuum interrupter is designed to satisfy OLTC operation condition, thus to ensure that OLTC has reliable

   quality and long operation life.

2 The vacuum interrupter are fixed completely in the insulation frame, it will not be interfered by the moving of

   contact.

3 Vacuum interrupter works as arcing contact, there are special mechanical contacts carry the current for long

   in main circuit, thus tap changer has good arc extinguishing capability and can be reliable operated for long

   time.

4 Adopting double-resistor transition structure in diverter switch, therefore it can be used for the transformer

   with bigger capacity.

5 Energy accumulating system is with compressed spring and adopting typical triggering principle, to make tap

   changer operation in reliable and stable.

Main technical data

Designation of CZ vacuum type on-load tap changer

CZ vacuum type OLTC varies in different phase number, maximum through current, highest voltage for
equipment and position number. In consequence, to distinguish type nuances, the designation of specific CZ
indicates clearly the values of above-listed variations as shown in below:

Structure and Conception

The CZ on-load tap changer is consisted of tap selector and diverter switch. Stationary contacts of the tap

selector and output conductor row are installed respectively on two insulation plates in parallel each other, and

the moving contacts of the tap selector is driven by screw bar to select tap terminal. Double stationary contacts

in parallel connection are adopted for the tap selector, so it is strong in current-loading capacity.

The take-off terminals of tap selector are connected to diverter switch via conducting leads and are classified

as odd side and even side. If the diverter switch runs at odd side, the moving contacts of the tap selector at

even side can be selected, and the diverter switch is driven by energy accumulator and switched into even side

after the selection completed. Thus, during next tap change, the moving contacts of tap selector at odd side are

to be selected.

The energy transmission of the tap changer is realized when the linked horizontal drive shafts run the

transmission mechanism of tap changer. This mechanism plays the role to activate moving contacts of the tap

selector to realize tap selection and at the same time put the energy accumulating mechanism into operation.

Once the tap selection finished, the energy accumulating mechanism triggers to make the diverter switch

execute tap change under load following specified program “close” and “open”.

The diverter switch consists of four vacuum interrupters, one pair of main mechanical contacts, two sets of

transition resistors and energy accumulating mechanism. The vacuum interrupters, fixed inside diverter switch,

are characterized as large switching capacity and long service life. The main contacts are made of pure copper

due to excellent load transmission capability of this material.

Transition resistors are made of Ni-Cr alloy which can resist extreme heat. The energy accumulating mechanism

adopts the principle of triggering after pass dead-point, which is reliable in terms of mechanical strength and

necessary speed.

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