Transformer Capacity Loss Tester

 

Definition and Applications

Definition: A transformer capacity and loss tester (also known as a transformer capacity tester or transformer capacity characteristic tester) is a high-precision, multifunctional measuring instrument used to measure a transformer’s rated capacity and loss parameters.

It combines the functions of a capacity tester and a loss parameter tester, capable of measuring parameters such as capacity, no-load current, no-load loss, load loss, and impedance voltage.

Applications: This instrument is primarily used for factory acceptance testing, on-site operational testing, and calibration of distribution or power transformers. It is particularly valuable in electricity metering and utility billing audits to verify whether a transformer’s nameplate capacity matches its actual capacity and to detect instances of unauthorized capacity increases by users.

For example, by measuring a transformer’s short-circuit impedance and losses, the actual capacity can be calculated and compared with the nameplate value, thereby identifying issues such as tampered capacity ratings

. The device is typically handheld or portable, equipped with a high-capacity battery that supports offline on-site testing. Its application scope covers distribution transformers (such as 10kV/0.4kV models with rated capacities ranging from tens to thousands of kVA) as well as small and medium-sized power transformers.

The core function of a transformer capacity and loss tester (also known as a no-load and short-circuit tester) is to simultaneously measure voltage, current, and phase, calculate power and losses through digital signal processing, and then determine capacity and derived parameters by analyzing no-load and short-circuit test data in conjunction with standard models.

1. Signal Acquisition and Conversion

Voltage Sampling: High-precision voltage transformers (PTs) or voltage dividers are used to convert high voltage into a 0–100 V low-level signal.

Current Sampling: Current transformers (CTs), Rogowski coils, or Hall sensors are used to capture high currents and convert them into low-level signals in the mA range.

Synchronous Sampling: Six-channel synchronous AC sampling captures three-phase voltage and current within the same cycle to eliminate phase errors.

Analog-to-Digital Conversion: A high-speed ADC converts analog signals into digital data, which is then sent to a DSP or MCU for processing.

Principle of Capacity Determination

The instrument incorporates national standard databases for S9, S11, S13, SCB, and other types. It compares the measured no-load loss P_0, load loss P_k, and impedance voltage U_k% with standard values, and uses an equivalent circuit model to calculate the rated capacity S_n.

2.Measurement Methods

1. No-load Test (Measure no-load loss P₀ and no-load current I₀%)

Wiring: Apply rated voltage U_n to the low-voltage side; leave the high-voltage side open-circuited

Procedure:

The instrument outputs a 50 Hz three-phase sine wave, adjusted to the low-voltage rated voltage

Measure input voltage U, current I₀, and power P₀

Calculate I₀% = (I₀ / I_n) × 100%

Physical Meaning: P₀ = Core Losses (Hysteresis + Eddy Current), reflecting core quality

2. Short-Circuit (Load) Test (Measure Load Loss P_k and Impedance Voltage U_k%)

Wiring: Short-circuit the three phases on the low-voltage side; apply voltage to the high-voltage side

Procedure:

Increase voltage until the high-voltage side reaches rated current In

Measure short-circuit voltage U_k and loss P_k

Calculate U_k% = (U_k / U_n) × 100%, and convert to 75°C

Physical significance: P_k ≈ winding copper loss; U_k% reflects short-circuit impedance and voltage drop

Oversea Brand

1. Megger (UK)

• Industry Position: Global leader in power testing
• Features: Extremely complete product line (full transformer diagnostics)
• Supports power factor, winding, resistance, ratio, frequency response, and other tests
• Representative Areas:
• Multi-functional test systems (TRAX)
• Power loss/dielectric loss testing (DELTA series)
• Advantages: High brand trust, IEC/IEEE standard compliance
• Disadvantages: High price, complex system

2. OMICRON (Austria)

• Industry Position: High-end intelligent testing expert
• Features: Extremely high degree of automation
• Integrated testing (capacity + loss + impedance + frequency response)
• Typical Product:
• TESTRANO 600 (fully automated transformer test platform)
• Advantages: Automation, high efficiency
• Disadvantages: Expensive

3. DV Power (Europe)

Features:

• Multi-functional analyzer (CT/PT/transformer)
• Multiple tests completed with a single connection (automatic switching)

Testing Capabilities:

Ratio, load, impedance, resistance, insulation, etc.

• Advantages: Better price-performance ratio than major European and American brands
• Disadvantages: Slightly lower brand influence

4. Vanguard Instruments (USA)

• Features: Focused on transformer testing (ratio, loss, capacity)

Durable equipment, wide range of field applications

• Advantages: High acceptance in engineering projects
• Disadvantages: Moderate level of automation

Domestic Brand

1. Goldhome Hipot

Positioning: Mid-to-high-end domestic brand

Core Product: Transformer capacity and loss tester (dedicated equipment)

Main Features: Specifically designed for determining the capacity of distribution transformers

Detects no-load loss, load loss, and short-circuit impedance

Automatically calculates capacity rating

Advantages: High cost-performance ratio

Easy to operate (suitable for rapid on-site testing)

2. Wuhan Gaodian

Features: Leading domestic manufacturer of power testing equipment

Products cover capacity and loss testing

Advantages: Mature technology

3. Huatian Power

Features: Focuses on transformer and high-voltage testing equipment

Advantages: Good cost control

1. Capacity and Load Loss Testing Wiring

This test determines the actual capacity and load-carrying capacity of the transformer.

High Voltage Side Wiring (Applied Voltage Side):

Tools Used: Three test clamps (yellow, green, red).

Wiring Steps: Connect the thicker wire from each test clamp to the corresponding color-coded Ia, Ib, Ic current terminals on the instrument panel.

Connect the thinner wire from each test clamp to the corresponding color-coded Ua, Ub, Uc voltage terminals on the instrument panel.

Clamp the test clamps to the A, B, and C phase terminals on the high voltage side of the transformer under test, according to their colors (yellow-green-red).

Low Voltage Side Wiring (Unapplied Voltage Side):

Operation: Use dedicated jumper wires to reliably short-circuit the A, B, and C phase terminals on the low voltage side of the transformer together.

Important Difference:

When performing a capacity test, the instrument's test power is provided internally.

When performing a load loss test, an external voltage regulator or power supply is required to power the instrument.

2. No-Load Loss Test Wiring

This test measures the core loss of a transformer.

Low-Voltage Side Wiring (Applied Voltage Side):

Wiring Steps: Clamp the three test clamps to the a, b, and c terminals of the transformer's low-voltage side according to their colors (yellow-green-red). Connect the thick and thin wires of the test clamps to the corresponding current and voltage terminals of the instrument, using the same method as described above.

High-Voltage Side Wiring (Unapplied Voltage Side):

Requirements: The high-voltage side of the transformer must be completely open; all terminals must be unconnected.

Power Supply: The no-load test requires an external voltage regulator to power the instrument, providing an adjustable sine wave power supply.

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