A relay test set is a specialised instrument used to test and verify the performance of protection relays in power systems. These relays protect transformers, feeders, transmission lines, generators, and motors by detecting faults and issuing trip commands to circuit breakers.
A relay test set simulates fault conditions by injecting precise currents and voltages into the relay under test. This allows engineers to verify the following:
- Pickup and drop‑off values
- Time–current characteristics
- Zone reaches and trip times for distance relays
- Differential and restraint characteristics
- Logic and output contacts
This guide explains how relay test sets work, the main types available, key specifications, typical test workflows, and how to select between two widely used models in India: the MP3000A and CRA160LHi relay test systems.
A relay test set (also called a protection relay test kit or relay testing system) is an instrument that:
- Generates controlled AC/DC currents and voltages
- Applies them to the relay’s current and voltage inputs
- Monitors the relay’s response (trip contacts, digital outputs, communication signals)
- Compares actual performance with expected settings and characteristics
Modern relay test sets are typically:
- Microprocessor‑based
- Controlled via PC software or an embedded HMI
- Capable of automated test sequences and report generation
They are used by:
- Utilities (transmission and distribution)
- Industrial plants and captive power stations
- Relay manufacturers and service centers
- EPC contractors and commissioning agencies
Relay test sets can be classified in several ways.
Single‑Phase Relay Test Set
- Outputs one phase of current and/or voltage.
- Suitable for:
o Overcurrent and earth fault relays
o Basic functional tests on multi‑phase relays (phase‑by‑phase)
Three‑Phase Relay Test Set
- Outputs three phases of current and voltage simultaneously.
- Required for:
o Distance relays
o Differential relays
o Directional and power‑based protection functions
Both the MP3000A and CRA160LHi are designed as universal three‑phase relay test systems, suitable for testing a wide range of protection functions.
Manual / Semi-Automatic Test Sets
- The operator sets values using knobs, switches, or a simple interface.
- Suitable for electro‑mechanical and solid‑state relays and basic functional checks.
Automatic Relay Test Systems
- PC‑controlled or embedded software‑based.
- Pre‑defined test modules for:
o Overcurrent (IEC/ANSI curves)
o Earth fault
o Distance (zone reach, R‑X characteristics)
o Differential (slope, bias, harmonic restraint)
- Features:
o Automated ramping and stepping
o Automatic measurement of operate time
o Pass/fail evaluation against settings
o Report generation
Both MP3000A and CRA160LHi fall into this automatic, software‑driven category, enabling repeatable, documented testing of numerical relays.
Key Specifications of MP3000A and CRA160LHi
Below are the typical characteristics that make these models suitable for utility and industrial relay testing. (Adjust exact values to match your official datasheets.)
MP3000A
- Three‑phase current output with high stability and accuracy.
- Three‑phase voltage output suitable for distance and directional relay testing.
- Suitable for testing:
o Overcurrent and earth fault relays
o Distance relays (zone reach and R‑X characteristics)
o Differential relays (with appropriate wiring and test modules)
CRA160LHi
- High‑current three‑phase output designed for high‑pickup relays and CT circuit testing.
- Integrated voltage outputs for distance and directional functions.
- Suitable for:
o High‑current overcurrent and earth fault relays
o CT saturation and burden tests (in conjunction with other instruments)
o Distance and differential protection testing
Both models support:
- Fine resolution of current and voltage steps for accurate pickup and timing tests.
- Simultaneous three‑phase output for realistic fault simulation.
Typical features for these classes of instruments:
- Current and voltage accuracy: in the range of 0.1%–0.5% of reading (depending on range and configuration).
- Phase angle resolution: fine steps for accurate directional and distance relay testing.
- Frequency control: around nominal 50 Hz with small variation for frequency‑dependent tests.
Refer to the official specification sheets for exact accuracy classes and resolution.
Both the MP3000A and CRA160LHi systems typically include:
- High‑resolution timing channels (1 ms or better) for trip time measurement.
- Digital inputs:
o To detect relay trip/close contacts (24/48/110/220 V DC or AC as supported).
- Digital outputs:
o To simulate breaker status, auxiliary signals, or initiate external devices.
These I/O capabilities are essential for:
- Automatic operation time measurement.
- Logic and scheme testing (e.g., auto‑reclose, interlocking).
These relay test sets are normally operated with Windows‑based or embedded software that provides test modules such as:
- Overcurrent / Earth Fault
o IEC and ANSI inverse curves (SI, VI, EI, LI, etc.)
o Definite time overcurrent
- Distance Protection
o Mho, quadrilateral, and custom impedance characteristics
o Zone reach and time verification
o R‑X plane testing
- Differential Protection
o Percentage differential with slope 1 and slope 2
o Harmonic restraint (2nd, 5th)
o Bias characteristics
- Directional and Power‑Based Functions
o Directional overcurrent
o Under/over voltage and under/over frequency
Advanced workflows may use XRIO files (where supported by the relay and software) to import relay settings and characteristic definitions directly into the test software. This reduces manual entry errors and speeds up commissioning.
- Designed for both lab and field use:
o Rugged enclosure for substation environments.
o Reasonable weight for portable operation by two engineers.
- Suitable for:
o Fixed test bays in utility workshops.
o Mobile relay testing vans and site commissioning.
Typical Relay Test Workflows with MP3000A and CRA160LHi
Below are common test workflows performed using these relay test sets.
1. Overcurrent and Earth Fault Relay Testing
Objective: Verify pickup current and time–current characteristic.
Typical steps:
- Connect test set current output to relay current input.
- Connect test set digital input to relay trip contact.
- Run an overcurrent ramp test:
o Increase current slowly until the relay operates.
o Record pickup current and operate time.
- Run time–current curve tests:
o Apply multiples of pickup (e.g., 1.2×, 2×, 5×, 10×).
o Measure operating time at each point.
- Compare results with relay settings and IEC/ANSI curves.
Both MP3000A and CRA160LHi support automated ramping and timing measurement, making these tests fast and repeatable.
Objective: Verify zone reaches, impedance characteristics, and trip times.
Typical steps:
- Connect three‑phase voltage and current outputs to the relay.
- Configure the test software with:
o Line impedance data
o Relay zone settings (reach, angle, time)
- Perform shot tests:
o Apply fault impedance at specific points inside/outside each zone.
o Verify correct zone operation and timing.
- Perform boundary search tests:
o Automatically find exact zone boundaries along different angles.
- Plot R‑X impedance trajectory to visualise relay behaviour during faults and swings.
For numerical relays that support it, XRIO files can be used to import zone settings and characteristic definitions into the test software, streamlining the setup.
Objective: Verify differential and restraint characteristics.
Typical steps:
- Connect test set currents to both sides of the differential relay (e.g., HV and CT secondary equivalents).
- Run pickup tests:
o Increase differential current until the relay operates with no restraint.
- Run slope tests:
o Apply varying levels of through current (restraint) and differential current.
o Verify operate/no‑operate boundary matches slope 1 and slope 2 settings.
- Test harmonic restraint:
o Inject 2nd and 5th harmonic components.
o Verify relay stability during inrush and over‑excitation conditions.
MP3000A and CRA160LHi, with their multi‑channel current outputs and precise control, are well suited for these tests when configured appropriately.
How to Choose Between MP3000A and CRA160LHi
Both models are capable of universal relay test sets. The choice depends on your specific needs.
1. Relay Portfolio and Test Requirements
- If your primary focus is:
o Distance and differential protection on transmission and sub‑transmission systems,
o Comprehensive automated testing with detailed reports,
Then a higher‑end configuration such as the MP3000A is often preferred.
- If your focus includes:
o High‑current overcurrent and earth fault relays,
o CT secondary injection tests at higher currents,
Then CRA160LHi, with its high‑current capability, can be advantageous.
2. Current and Voltage Requirements
- Evaluate:
o Maximum pickup currents of the relays you test.
o Whether you need very high secondary currents for CT testing or special applications.
- Match these to the rated output ranges of MP3000A and CRA160LHi.
- Confirm which test modules you need:
o Distance, differential, overcurrent, directional, etc.
- Ensure the software package supplied with your chosen model includes all required modules and supports your relay types (ABB, Siemens, Schneider, GE, Alstom, etc.).
4. Portability and Site Conditions
- For extensive field testing and mobile labs:
o Compare weight, dimensions, and power requirements of both models.
- For lab or fixed installation:
o You may prioritise higher power and more channels over portability.
- Consider:
o Initial purchase cost.
o Calibration, maintenance, and software upgrade costs.
o Availability of local support and training.
A life‑cycle view often favours a slightly higher initial investment if it significantly reduces test time and improves report quality.
Relay test sets and the testing process should align with relevant standards, such as:
- IEC 60255 series – Measuring relays and protection equipment
- IEC 61850 – Communication for substation automation (for advanced testing)
- IEEE C37 series – Protective relay standards
- Relevant Indian Standards (IS) for testing and safety
Ensure your MP3000A or CRA160LHi system is calibrated and traceable to national standards, and that your test procedures are documented and auditable.
When using relay test sets like MP3000A and CRA160LHi:
- Always follow the manufacturer’s safety instructions.
- Use proper personal protective equipment (PPE) when working in substations.
- Ensure correct earthing and isolation before connecting test leads.
- Verify that test currents and voltages are within the relay’s and CT/VT circuit’s rated limits.
- Use appropriate fuses and protection in test circuits.
Where to Buy MP3000A and CRA160LHi Relay Test Sets
If you are looking for reliable relay test sets based on the MP3000A and CRA160LHi platforms for utility or industrial applications, you can explore our commercial offerings:
- IndiaMART listing:
Relay Test Set (MP3000A ) – IndiaMART Product Page
MP3000A Protective Relay Test Set - Myriad Industrial Solutions product page:
Protection Relay Test System – MP3000A / CRA160LHi
Test set for advanced relays for precision protection systems - Our relay test systems support:
- Overcurrent, earth fault, distance, and differential relay testing
- Automated test sequences and report generation
- Optional XRIO‑based workflows for supported numerical relays
For detailed technical notes on specific test workflows (such as distance relay testing with XRIO files), see our related articles on electricaltestkit.com.
Related Articles on electricaltestkit.com
To go deeper into specific topics, you may find these articles useful:
- “XRIO Characteristics Reconstruction for Distance Relay Testing”
- “How to Test Distance Relays Using a Three‑Phase Relay Test Set (MP3000A / CRA160LHi)”
- “Automated Relay Testing Workflows for Numerical Relays”
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