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

Below is the **English translation with full preservation of structure, HTML tags, lists and emphasis**.

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In this blog, we explain **per measurement** what the SUWI-120 does, **what exactly is measured**, and **why each measurement is essential in real-world applications**.

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 exact moment at which the relay operates.

Why is this important?

Protection relays form 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

In addition to the ratio, the SUWI-120 also 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**, allowing even complex transformer configurations to 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 simulate realistic operating conditions.

Why is this important?

Increased contact resistance results in:

• localised heating
• accelerated ageing
• increased risk of failure

By measuring with high current, issues are detected that remain invisible when using 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

Additionally, the SUWI-120 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 indicates:

• wear
• contamination
• adjustment or alignment issues

Graphical analysis shows exactly 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

In addition to automated tests, the SUWI-120 also offers manual test modes, allowing you to:

• 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

Why this makes the difference in one single system

In practice, the SUWI-120 means:

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

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

Summary

The SUWI-120 is not an “all-in-one” device simply because it does many things, but because the measurements are **logically connected** — from relays to transformers and from circuit breakers to contacts. This makes the system particularly suitable for **substation testing where both overview and technical depth are required**.

If you want to see these measurements in practice or integrate them into your test strategy, this is exactly the type of system that **reduces complexity instead of adding it**.

Also available for rental from IONIO – from Q1 2026

Good news 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 access to all measurement capabilities of the SUWI-120 — relay timing, transformer turns ratio, micro-ohm measurements and circuit breaker analysis — without capital investment. Ideal 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 assistance with the correct test setup

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