The SUWI-120 as one system for the entire substation

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

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

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

Technical details

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

What is measured?

The contact resistance of:

• circuit breaker contacts
• busbars
• shunts and electrical connections

The SUWI-120 measures with a DC test current up to 120 A. That is well above the 50 A minimum named in IEC 62271-1 and enough to break through oxide layers on the contacts.

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

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
• contact times per phase (3-phase)

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

The contact times and the coil current curve per phase show whether a breaker operates too slowly or unevenly. The SUWI-120 has no input for a motion transducer. For motion analysis of the mechanism, use the CIBRE-30 or CIBRE-60.

Technical details

• time error 0.05% of reading ± 0.1 ms
• internal and external triggers

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

You read out the results via USB or Ethernet in the included DMP software.

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, what matters most is reliable decisions based on consistent measurement data.

On top of that, the SUWI-120 is built for outdoor work: IP67 with the lid closed, an operating temperature of -10 to +60 °C and a weight of 10.7 kg.

• Grid operators and utilities: periodic inspection of circuit breakers, protection relays and transformers.
• Installation and service companies: commissioning of new switchgear, FAT and SAT.
• Industry: contact resistance and breaker timing in your own distribution system.
• Fault response teams: fast checks of relays and breakers, and of transformer turns ratio, phase angle and polarity, with one instrument. For a full transformer diagnosis, the TRAN-203 is the right tool.

The SUWI-120 is broad: four substation tests in one. If your focus is on transformers, look at the TRAN-203. It measures turns ratio up to 50,000 and winding resistance at 20 A DC, controls the tap changer (OLTC) and performs a heat run. Read more in our blog about the TRAN-203.

For extended breaker analysis with motion analysis, there is the CIBRE-30 (3 contacts) and the CIBRE-60 (6 contacts).

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.

The SUWI-120 is available for purchase from IONIO, with a 12-month warranty and the DMP software included. If you prefer not to invest, you can also rent it.

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

the SUWI-120 is available for rental from IONIO.

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.

Request a quote · Request rental · Buy the SUWI-120 · Rent the SUWI-120