A transformer with staged windings is switched by moving a contact pick-up across the winding (TW). Selector connections (M1, M2) extend to the neighbouring tapping points (T1, T2). The connections are coupled to the contents (SA, SB) of a change-over switch (S). The switch has a moving contact (Sm) and a common contact (Sc) coupled to a main stage (H). The neutral point (N) connects to a resistor vacuum valve (W) with a resistor (R) in series. The movable contact (Sm) changes over between adjacent contacts, the current being limited by the resistor. ADVANTAGE - Reduces possibility of contact arcing.

Stage switch changing coils of power electrical transformer - couples adjacent stages to tapping contacts with movable contact engaging common contact and having current limiting resistor.

An arrangement of an on-load change-over switch of a sequence switch for uninterrupted switching of the regulating coil of a transformer. On-load change-over switching is usually effected with mechanical switch elements, which entails undesirable burn-up of the contacts and contamination with oil. In other known embodiments, on-load change-over switching is achieved using mechanical switching elements and thyristors. The main drawback of these arrangements is the high cost of the control elements, which are prone to failure. According to the invention, the load current is supplied to a common branch line (16) through a lower or upper coil tapping point (11, 12) of a regulating step (13) of a regulating coil and at least two selector contacts (14, 15) and two permanent contacts (9, 10). Change-over switching from the lower to the upper coil tapping point and vice versa is effected by a change-over switch (5) which switches the load current briefly to a discharge circuit (17), arranged between the root connection (6) of the change-over switch and the common branch line. The discharge circuit can comprise, for example, two thyristor circuits (2, 3) whose thyristors (2a, 2b, 3a, 3b) are connected in anti-parallel, one of the transistor circuits being connected in series with a transition resistance.

Thyristor on-load change-over switch

A retrofit diverter switch which has a mechanical and electrical interface that is compatible with the existing designs is provided. The diverter switch may include a vacuum switch. The feature where the mechanical and electrical interface is compatible enables a retrofit from traditional On Load Tap Changers to a vacuum based on Load Tap Changers. The diverter switch may be retrofitted into existing tap changer housings. Retrofitting from traditional to vacuum based, traditional to vacuum based and up rating, and vacuum up rating may be possible. Also, the diverter switch may include modular components that allow for easy customization of the diverter switch for different applications.

Vacuum based diverter switch for tap changer

A tap changer and a method for measuring a contact sequence of a tap changer is provided. The tap changer comprises a cylinder and a shaft that is rotatably arranged inside the cylinder, the cylinder is provided with fixed contacts, the shaft is provided with a contact circuit facing the cylinder and including mechanical contacts, which mechanical contacts are adapted to selectively mate with the fixed contacts of the cylinder upon rotation of the shaft, the contact circuit also includes at least two measuring points for measuring the function of the contact circuit. The tap changer comprises at least one measuring contact device, which is electrically connected to the respective measuring points in the contact circuit, and which the measuring contact device is arranged inside the shaft. This facilitates access to the measuring points of the tap changer.

Measuring Contact Sequence In A Tap Changer

The invention relates to a gearbox for a tap changer. The gearbox has an input drive shaft (1) arranged to be connected to a motor. The gearbox also has a diverter switch drive output (3) with a diverter shaft (31). The diverter switch drive output (3) is arranged to be connected for actuation of breakers in a diverter switch of the tap changer. According to the invention the gearbox further has first (4) and second (5) selector arm drive outputs arranged for actuation of a tap selector of the tap changer. It also has reduction gear means (71) connecting the input drive shaft (1) to the diverter switch drive output (3) and to each of the selector arm drive outputs (4, 5). Further the gearbox has timing connection means arranged to connect the reduction gear means (11, 71) to each of the selector arm drive outputs (4, 5). The invention also relates to a tap changer having such a gearbox and to a transformer provided with such a tap changer.

A gearbox for a tap changer, a tap changer and a transformer

An on-load tap changer wherein diverter switch circuits each of which is a series connection of a main switch A, B and an auxiliary switch C, D are connected between an output terminal (13) and a plurality of tap selecting arms (1, 2) and wherein resistors R1, R2 are employed as current-limiting bridge elements. The main switch has a movable contact (7, 8) connected to the output terminal, the auxiliary switch has a movable contact (11, 12) connected to a stationary contact (5, 6) of the main switch and a stationary contact (9, 10) connected to the odd-input terminal (3,4) and the current-limiting resistors are respectively connected in parallel with the main switches. The switches are preferably vacuum switches.

Yuji Mihara

Papers

On-load tap changer

Development of 500kV Liquid Cooled Gas Insulated Transformer