Measurements and tests with the SUWI-120 – one system for the entire substation

This blog covers each measurement the SUWI-120 performs: what it measures and why it matters in practice.

Protection Relay Timing Measurements

What is measured?

The pickup and operating time of protection relays, such as:

• overcurrent relays
• overvoltage relays
• directional overcurrent relays
• frequency relays

The SUWI-120 injects an adjustable current or voltage and measures the moment the relay operates.

Why is this important?

Protection relays are the first line of defence in a power network. Switching too slowly leads to damage; switching too fast causes unnecessary outages. With the SUWI-120 you verify:

• correct pickup value
• proper time characteristic
• repeatability across multiple tests

Technical details:

• AC current up to 110 A, DC up to 120 A
• AC voltage up to 150 V, DC up to 220 V
• adjustable frequency and test profiles

Transformer Turns Ratio Measurement

What is measured?

The ratio between primary and secondary windings of:

• current transformers (CT)
• voltage transformers (VT/PT)
• single-phase and three-phase power transformers

Besides the ratio, the SUWI-120 measures:

• phase angle
• polarity
• ratio deviation in %

Why is this important?

A small error in turns ratio can have major consequences:

• incorrect measurement values in the network
• incorrect protection operation
• phase imbalance

The SUWI-120 supports both IEC and ANSI vector groups, so complex transformer configurations can be tested correctly.

Technical details:

• test voltages from 1 V up to 100 V
• ratio range from 0.8 to 10,000
• automatic calculation of deviations

Contact and Low-Resistance Measurement (Micro-ohm)

What is measured?

The contact resistance of:

• circuit breaker contacts
• busbars
• shunts and electrical connections

The SUWI-120 uses high DC test currents to approximate realistic operating conditions.

Why is this important?

Increased contact resistance results in:

• localised heating
• accelerated ageing
• increased risk of failure

Measuring at high current reveals issues that stay invisible with low test currents.

Technical details:

• test current up to 120 A DC
• measurement range up to 5 Ω
• stable static measurement

Circuit Breaker Timing Measurements

What is measured?

The mechanical operating times of circuit breakers:

• opening (O)
• closing (C)
• O-C, C-O and O-C-O sequences

The SUWI-120 also measures:

• trip and close coil currents
• phase asymmetry (delta time)
• graphical time and current curves

Why is this important?

Circuit breakers rarely fail electrically; failures are usually mechanical. Delayed or uneven movement points to:

• wear
• contamination
• adjustment or alignment issues

Graphical analysis shows where in the operating sequence the problem occurs.

Technical details:

• timing accuracy ±0.1 ms
• internal and external triggers
• automatic phase comparison

Manual and Combined Test Modes

Besides automated tests, the SUWI-120 has manual test modes, which let you:

• simulate specific scenarios
• analyse non-standard components
• perform tests outside standard procedures

All results are stored with:

• test header (station, operator, date)
• numerical values
• graphs and screenshots

One system for the whole substation

In practice, the SUWI-120 means:

• less equipment to transport
• reduced risk of interpretation errors
• one consistent measurement method
• faster testing and reporting

For utilities, service companies and maintenance teams, the last point matters most: reliable decisions based on consistent measurement data.

Summary

The SUWI-120 groups its measurements because they are logically connected, from relays to transformers and from circuit breakers to contacts. That makes it suitable for substation testing where you need both overview and technical depth in one device.

If you want to see these measurements in practice or fit them into your test strategy, this is the type of system that keeps a test campaign simpler rather than adding another box.

Also available for rental from IONIO – from Q1 2026

For organisations that want to test but do not (yet) want to invest:

the SUWI-120 will be available for rental from IONIO starting Q1 2026.

This gives you all measurement capabilities of the SUWI-120 — relay timing, transformer turns ratio, micro-ohm measurements and circuit breaker analysis — without capital investment. Useful for:

• temporary projects or maintenance outages
• FAT/SAT testing during new builds or substation refurbishments
• additional test capacity during peak workloads
• validation or comparison with existing test equipment

The tester is supplied:

• calibrated and fully tested
• ready for immediate use
• with technical support from IONIO, including help with the correct test setup

This combines the technical depth of the SUWI-120 with the flexibility of rental.