OLTC/DETC
for Distribution
Transformers
OLTC/OCTCs for Distribution Transformers
On-load and De-Energized Tap-Changers for Distribution Transformers
- Dry Vac
- l type
- oc-series
DRY VACUUM TYPE (Dry VAC)
The Dry VAC has a maximum rated through-current of 500A and a max. Rated step voltage of 900V for linear voltage adjustment in nine to seventeen operating positions.
Each Dry VAC module contains a tap selector and diverter switch for high-speed resistor type tap change operation in a compact design.
The movable tap selector contact system and the diverter switch, with the spring-energy accumulator, are driven by a screw spindle.
Vacuum Interrupters are used as the switching elements which guarantees maintenance-free operation and prolonged life.
It contains all the devices required for local and remote control, for the remote display of operating positions as well as the electrical and mechanical end position limits.
As standard equipment, a motor drive unit which functions according to the step-by-step switching principle is provided to mechanically operate the on-load tap-changer.
Its protective housing makes the motor drive unit suitable for outdoor installation, and in case of a dry-type transformer in encapsulated design it can be mounted outside the transformer tank.
Vacuum-interrupters, based on the proven vacuum technology, are used as load-switching contact elements. They guarantee excellent electrical and mechanical properties over an extremely long lifespan.
Its protective housing makes the motor drive unit suitable for outdoor installation, and in case of a dry-type transformer in encapsulated design it can be mounted outside the transformer tank.
Vacuum-interrupters, based on the proven vacuum technology, are used as load-switching contact elements. They guarantee excellent electrical and mechanical properties over an extremely long lifespan.
Electrical parameters | |||||||
TYPE | Current Rating (A) | Voltage Variants | BIL kV/kVp | Max. Rated Step Voltage (Volts) | Max. Operating Position | ||
Three Pole | Single Pole | Voltage Level (kV) | Vector | Linear | |||
DRY VAC | 200, 300 & 500 | 200, 300 & 500 | 11 | Y, D | 85/200 | 900 | 17 |
33 | Y, D | 900 | |||||
L TYPE
Integrated drive mechanism.
Designed for 500,000 operations.
No barrier board required.
No huge sealing area required, hence leak free.
Transformer size becomes very slim.
No conservator required and hence no piping costs.
Between 50,000 operations, no maintenance is needed.
Total freedom from menace of barrier board related problem.
Only half an hour time required for the inspection of OLTC.
Electrical parameters | |||||||
TYPE | Current Rating (A) | Voltage Variants | BIL kV/kVp | Max. Rated Step Voltage (Volts) | Max. Operating Position | ||
Single Pole | Voltage Level (kV) | Vector | Linear | Pre-Selector | |||
L TYPE | 200 | 11, 22 & 33 | Y, D | 80/250 | 825 | 9 | 17 |
SERIES- OC (FOR Distribution Transformers)
SERIES – OC-R (FOR DISTRIBUTION TRANSFORMERs)
| Voltage Class | 11 to 66kV |
| Current Rating | 50 to 250Amps |
| Step Voltage | 1.5% per step |
| No.Of Taps | 05 / 07 / 09 |
| No.Of Phase/Deck | 03 / 06 / 09 / 12 |
| Connection | Bridge Type |
| Operation | Manual |
| Mounting | Horizontal Mounting |
| Cooling Medium | Transformer Oil |
Base Type
(core frame Fixing)
SERIES – OC-t (FOR DISTRIBUTION TRANSFORMERs)
| Voltage Class | 11 to 33kV |
| Current Rating | 50 to 250Amps |
| Step Voltage | 1.5% per step |
| No.Of Taps | 05 / 07 / 09 |
| No.Of Phase/Deck | 03 / 06 / 09 / 12 |
| Connection | Bridge Type |
| Operation | Manual |
| Mounting | Horizontal Mounting |
| Cooling Medium | Transformer Oil |
Tie Rod Type
(Core Frame Side Fixing)
SERIES – OC-l (FOR DISTRIBUTION TRANSFORMERs)
| Voltage Class | 11 to 36kV |
| Current Rating | Upto 100Amps |
| Step Voltage | 1.5% per Step |
| No.Of Taps | 5 & 7 |
| No.Of Phase | 3Phase |
| Connection | Bridge Type |
| Operation | Manual |
| Mounting | Horizontal Mounting |
| Cooling Medium | Transformer Oil |
Distribution Transformers - frequently asked questions
How do OLTCs maintain voltage stability in distribution transformers?
 OLTCs in distribution transformers automatically adjust winding taps under live conditions to stabilize consumer-side voltage. This prevents undervoltage and overvoltage events in the consumer-side networks.
Why are vacuum OLTCs increasingly adopted in urban distribution grids?
Vacuum OLTCs eliminate oil-based arcing, enabling compact designs with minimal maintenance. This is critical for densely populated substations where safety, space efficiency, and service continuity are priority requirements.
How does OLTC integration reduce lifecycle cost in distribution transformer fleets?
 Automated tap regulation reduces manual intervention, oil replacement cycles, and unscheduled shutdowns. This improves transformer availability and lowers the total cost of ownership for utility operators.
Which OLTC technologies are applied in modern distribution transformer design?
 D-VAC OLTC systems for dry-type transformers and V-Vac OLTCs for power transformers apply sealed vacuum switching for maintenance-free operation. At the same time, L-Type OLTCs are engineered for higher current duty distribution networks requiring robust voltage control.
When should OCTC be selected for distribution transformer voltage control?
OCTC solutions are selected where voltage settings remain stable for long periods, and adjustments can be completed during maintenance windows, offering a cost-efficient alternative to automated OLTC systems.
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