Transformer Basics
This type of transformer is most commonly mounted on poles for residential overhead service.
What is a single‑phase pole‑mounted transformer?
This transformer configuration is commonly used to serve single residences.
What is a single‑phase transformer?
This voltage is measured from L1 to Neutral on a residential service.
What is 120 volts?
These two voltages are 180 degrees apart in a single‑phase 120/240 V system.
What are L1 and L2?
You have 240 V across L1–L2 but zero volts from L1 to Neutral.
What is an open secondary neutral?
This is the typical primary voltage supplying single‑phase aerial distribution transformers.
What is 7.2 kV?
This transformer setup uses three individual transformers instead of one unit.
What is a three‑phase transformer bank?
This voltage is measured from L1 to L2 on a split‑phase system.
What is 240 volts?
Draw the voltage vectors for a single‑phase split‑phase transformer secondary.
Incorrect phase rotation will cause this issue in motors.
What is reverse rotation?
This transformer bushing provides the neutral connection on the secondary side.
What is X2 (center tap)?
This three‑phase connection can operate with only two transformers if one fails.
What is open‑delta?
This secondary voltage configuration is written as 208Y/120 V.
What is a wye‑connected three‑phase system?
In a balanced three‑phase system, voltage vectors are separated by this angle.
What is 120 degrees?
This condition can occur if one transformer in a three‑phase bank is reversed.
What are circulating currents?
This transformer component protects against voltage surges caused by lightning.
What is a lightning arrester?
This transformer connection has no neutral on the primary side.
What is delta?
This voltage relationship shows two equal voltages that are 180 degrees apart.
What is split‑phase voltage?
Draw the secondary voltage vectors of a 208Y/120 V system.
This field issue can cause overheating without a visible fault.
What is incorrect polarity?
This type of transformer winding provides both 120 V and 240 V from a single secondary.
What is a center‑tapped secondary?
This three‑phase transformer connection provides a neutral on the secondary.
What is wye?
This causes equal voltage readings phase‑to‑phase but incorrect phase‑to‑neutral readings.
What is an open or broken neutral?
This amount of phase shift exists between a delta‑wye transformer’s primary and secondary.
What is 30 degrees?
This can result from improper phasing during transformer installation.
What is equipment damage or phase‑to‑phase fault?