Transformer Polarity and Voltage Calculations

Refresher Course on Distribution Transformers

• Distribution transformers are vital components in electrical power systems.
• The MERALCO (Manila Electric Company) system involves voltage conversion across various stages (generation, transmission, sub-transmission, and distribution).
• Key voltages within MERALCO's system are 13.8kV, 230kV, 69kV, 115kV, 13.2/7.62kV, and others.
• Transformer nomenclature (nameplate and company number) and workshop procedures are crucial for maintenance and operation.
• Transformer taps allow adjusting voltage levels.
• Transformer polarity (additive or subtractive) impacts interconnected transformer operations.
• Correct connections for secondary systems are critical to avoid common errors.
• Essential reminders for safe distribution transformer installations are vital for preventing electrical hazards.
• Typical distribution transformer parts include primary and secondary bushings, KVA rating, company number, and nameplate.
• A distribution transformer nameplate details kVA rating, secondary voltage rating, voltage rating per tap position, and polarity.

Overview of MERALCO System

• MERALCO's system efficiently distributes electrical power.
• Electrical power proceeds from generation through transmission, sub-transmission, and distribution.
• Different voltages are used at each stage of the system, indicating voltage transformation.

Outline

• The course outlines key topics relating to distribution transformers.
• Topics include transformer nomenclature, workshop practices, transformer taps, and transformer polarity.
• Other vital topics include transformer connections, troubleshooting/troubleshoots, secondary system connections, and installation reminders.

Typical MERALCO DT

• Images illustrate typical MERALCO distribution transformer components.
• This includes primary and secondary bushings, KVA ratings, and company numbers on the nameplate.

DT Nameplate Sample

• Nameplates provide essential transformer specifications.
• These crucial specifications include KVA rating, secondary voltage rating, and polarity (additive or subtractive).

DT Company Number Coding System of MERALCO

• Prefixes: The old and new systems for coding distribution transformers are illustrated.
• Suffixes: Key voltage ratings (120/240, 139/277, and others) are associated with corresponding code letters.

Difference Between 120/240 & 240/120-Volt Ratings

• 120/240 configurations allow connecting windings in series or parallel (i.e., dual voltage).
• The 240/120 configuration is suitable for different wiring, such as two-wire or three-wire applications.

External Tap-Changers

• The operation describes the procedure for changing tap positions on external tap changers.

Other Types of External Tap-Changers

• Different designs of external tap changers are represented by various images.

Internal View of a DT With an External Tap-Changer

• An image illustrates the inner parts of a distribution transformer featuring an external tap changer.

Internal Tap-Changers & Rotary Tap-Changers

• Illustrations display the internal components of transformers with internal tap changers.

Schematic Diagram of a Dual Voltage Transformer

• These diagrams show how dual voltage taps in transformers work.
• Diagrams explain connections for both 120/240 and 139/277 configurations.

Samples of DTs With Dual Voltage Tap

• Images of distribution transformers showcase dual voltage tap features.

Transformer Polarity Convention

• The polarity convention for different transformer ratings is outlined in this section.
• Different transformer polarities (additive or subtractive) affect systems' operation.

Terminal Markings of DTs

• Clear diagrams showing terminal markings on additive and subtractive polarity DTs are present.

Polarity of DTs

• Various examples of kVA and voltage ratings highlight the additive or subtractive polarity.

Polarity Testing of a DT

• Procedure for determining whether a transformer has additive or subtractive polarity are illustrated in diagrams.

DT Connections Used by MERALCO

• Charts listing the different connections used for distribution transformers by MERALCO are included.

Single-phase Connection

• Diagrams illustrate single-phase connections.
• Details include line-to-neutral and line-to-line connections for both additive and subtractive polarities.

Open-Wye, Open-Delta Connection

• These illustrate connection circuits for transformers with different polarities.

Common Errors in Open-Wye, Open-Delta Connections

• Diagrams showcase common errors during Open-Wye, Open-Delta connections.

Wye-Delta Connection

• This section describes Wye-Delta connections.

Common Error in Wye-Delta Connections

• This section details potential errors during Wye-Delta connections.

Corrected Error in Wye-Delta Connection

• This section demonstrates corrected wiring configurations for potential Wye-Delta connection issues described above.

Wye-Wye Connection

• Detailed wiring configurations for Wye-Wye connections, for both 240-volt and 480-volt services, and appropriate polarities, are shown.

Open-Delta, Open-Delta Connection

• Diagrams outlining Open-Delta, Open-Delta connections for different polarities are included.

Common Error in Open-Delta, Open-Delta Connections

• Diagrams highlight and explain common wiring mistakes during Open-Delta Open-Delta connections.

Delta-Delta Connection

• Diagrams detailing Delta-Delta connections are detailed for both subtractive and additive polarities.

Single-Phase 240V, Line-to-Ground Secondary System

• This section describes a single-phase 240V, line-to-ground secondary system.

Open-Wye, Open-Delta Connection for 3-Phase, Corner-Grounded Delta Secondary

• Diagrams illustrate the Open-Wye, Open-Delta connection for a 3-phase, corner-grounded delta system.

Wye-Delta Connection for 3-Phase, Corner-Grounded Delta Secondary

• Diagrams illustrate the Wye-Delta connection in a 3-phase, corner-grounded delta secondary system.

Reminders on DT Installation

• This section offers instructions and reminders for new installations.
• Important points include inspecting the transformer, verifying specifications, adhering to standards, ensuring the system is de-energized, and carrying out voltage checks before energizing.
• Additional insights for replacing distribution transformers are included.

Available DT Banks at the Training Grounds

• A list of available distribution transformer banks at a training facility is given.

This quiz explores various concepts related to transformer polarity, including additive and subtractive configurations, voltage calculations, and connection types. Test your understanding of Wye-Delta and Open-Delta connections and how they influence secondary voltages. Perfect for students and professionals looking to deepen their knowledge of electrical transformer operations.