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Should You De-Energize Transformers When Changing Taps?

Since the input power fed into a transformer may be lower or higher than the intended rate, transformers require adjustments to produce the correct secondary voltage. These fluctuations can occur for various reasons, including a power drop across a long distribution line or excessive consumption from one or more facilities. Since it is impractical and inefficient to make adjustments across an entire utility network, tap changers are a more effective way to remedy the situation at the problem point.

To ensure safety, operators should only change taps and use off-load or no-load tap-changing devices when a transformer is de-energized or not operating. On-load tap changers allow operators to make voltage changes without disrupting the power supply.  Also called load tap changers.  Typically used on the much larger units.

What Is a Transformer Tap?

Taps make changing a transformer’s voltage ratio possible. These connection points along a transformer’s winding allow adjustments to the primary coil, ensuring the correct secondary voltage. These taps are adjustable at the coils with a tap-changing device or manually using a jumper lead.

The main responsibility of a transformer is changing the primary voltage into the specific secondary voltage needed for an application. If the voltage feeding into a unit differs from the transformer’s input rating, the secondary voltage the transformers produce will follow suit. Tap changers are necessary because they protect sensitive equipment unable to handle even the slightest voltage fluctuations from damage.

How Do Tap Changers Work?

Using a tap-changing device requires the operator to choose the setting closest to the incoming power supply’s voltage. Changing a tap engages or disengages small sections of the primary windings to achieve the correct voltage needed for a specific application.

On padmount transformers, off-load or no-load tap changers are often in the primary high-voltage cabinet and use rotary controls for operation. These tap-changing devices should only be operated when the transformer is de-energized to ensure maximum safety. Many of these devices feature a chart that lists the taps and the adjustments needed above or below a transformer’s rating.

Off-load or no-load tap changers are ideal for applications with voltage fluctuation that is infrequent or small in magnitude, while on-load or load tap changers or voltage regulators are best suited for more frequent voltage fluctuations.

Since tap connections on dry type transformers are easily accessible, users can change off-load taps manually instead of using a tap-changing device. These connections are only adjustable when the transformer is not operating or de-energized.

Contact ELSCO Transformers to Learn More

Contact ELSCO Transformers to Learn More

At ELSCO Transformers, our new padmount transformers have all the accessories you need for optimal operation, including upgraded rotary-type tap changers. Our experts can answer your questions and help you choose a transformer most beneficial to your operational requirements. We also offer many other transformer services, from retrofitting and custom bus work to repairs and emergency replacements.

Please contact us with questions or complete a quote request form for pricing.