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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Which one is connection type of PT?
A-A
V-V
C-C
G-G
V-V
Quick Summary: Potential Transformers (PT) are used for measuring high voltages by stepping them down to standard secondary voltage levels. The V-V (Open-Delta) connection is widely used for 3-phase PTs as it provides a cost-effective solution requiring only two PT units instead of three to measure line-to-line voltages.
Potential Transformers (PT) are used for measuring high voltages by stepping them down to standard secondary voltage levels. The V-V (Open-Delta) connection is widely used for 3-phase PTs as it provides a cost-effective solution requiring only two PT units instead of three to measure line-to-line voltages.
Vsecondary=Vprimary×NpNs — Transformation ratio of PT
SV−V=31SΔ−Δ — Capacity of V-V connection
The V-V connection involves connecting two single-phase transformers in an open-delta configuration. This setup allows the transformation of 3-phase voltages by utilizing the relationship VAB+VBC+VCA=0, where the missing third phase voltage is provided by the vector sum of the other two phases. While it is economical, it has a reduced capacity compared to a full delta-delta configuration, limited to 57.7% of the total kVA rating of three similar transformers.
Used for metering and relaying in medium and high voltage systems.
Requires only two potential transformers, making it more economical.
The secondary side voltages maintain the correct phase displacement of 120°.
Used when the load is primarily line-to-line voltage measurement.
Lower capital cost due to fewer units.
Suitable for emergency supply if one transformer fails in a Delta-Delta bank.
Lower total kVA capacity than a full three-phase bank.
Increased risk of unbalance if the load is not perfectly balanced.
Voltage measurement in three-phase power circuits.
Protection relaying for phase-to-phase faults.
PTs are always connected in parallel with the lines they monitor.
A-A, C-C, and G-G are not standard industrial notations for PT connection types.
B is correct — The V-V connection, also known as the open-delta connection, is a standard and economical method used for PT configurations in three-phase systems.
Remember that PTs act as ideal voltage sources and must NEVER be short-circuited on the secondary side, unlike CTs which must never be open-circuited.