Conventionally, most of the power transformers worldwide have been using on-load tap changers that apply high-speed resistor switching and tungsten-copper alloy contacts to extinguish in oil at zero-current point. In such cases, oil carbonisation and contamination will become matters of concern because of the contact burning and loss increase after frequent operations, which will require more maintenance.

The 21st century being an era of vacuum and power information technology, the tap changers are also facing a revolution now. In order to meet the demand of modernisation of power systems, to completely solve oil contamination problems, improve mechanical and electrical life of tap changers, reduce maintenance and ensure reliable and safe operations, HMG Power Systems has developed VCM type oil-immersed vacuum on-load tap changer.

VCM type vacuum on-load tap changer is an up-to-date product developed especially for the update and retrofit of the existing CM type tungsten-copper alloy contact switching tap changer.

Features of VCM Type Vacuum OLTC

• VCM type has the same operation principle of CM type; both are double-resistor transition switching
• VCM type has the same overall dimension with CM type (or M type), which will facilitate an easy on-site replacement of the whole tap changer or diverter switch only (see Figure 2), also will reduce cost of retrofit in power network for CM type
• VCM type uses vacuum interrupter to replace the tungsten-copper alloy contact in CM type switching mechanism, which will avoid oil carbonization and contamination, thus to improve the insulation strength of oil and contact life, and no need to filter oil or change oil, which reduces cost
• VCM type vacuum on-load tap changer is 300,000 operations maintenance-free, which will greatly reduce maintenance cost
• VCM type vacuum on-load tap changer carries long time current by special mechanical shunt main contacts, and only carries short-time current by vacuum interrupter, which enables higher over-current withstand capacity. All vacuum interrupters are fixed in stationary position and will not mis-operate.

VCM Type Vacuum On-load Tap Changer Technical Data

VCM type vacuum on-load tap changer is applicable for all kinds of transformers with maximum three phase rated through current of 600 A, maximum step voltage of 3300 V, and rated voltage of 63-220 kV. The operation positions of this tap changer are 18 (without change-over selector) or 35 (with change-over selector), as seen in details in Table 1.

(Contact: HMG Power Systems Pvt Ltd, Bangalore. Mobile: 099805-42552. Tel: 080-23579157, 654660766. Fax: 91-80 -23579152. Email: balaji@hmgpower.com)