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On-Site Current Transformer Testing

Current Transformers (CT’s) are used for both Measuring and Protection purposes connecting high power switchgear to the secondary device.

We have now invested in a state of the art CT Analyser which can be used both in the factory for CT tests at the manufacturing stage or on site to provide tests to confirm the specification of the installed CT – either measuring or protection CTs. The CT Analyser (manufactured by Omicron) automatically determines all the relevant CT values and can compare the results with the selected standard.

The following values can be tested using the CT Analyser

  • CT Ratio
  • CT Phase Angle
  • CT Excitation & Saturation
  • Burden Impedance
  • Winding Impedance
  • Saturated Inductance
  • CT Polarity

Instrument Transformers Limited can provide these tests using this CT Analyser typically throughout the UK with their experienced test engineers. Whether it is an industrial or commercial installation – we provide the customer with a test report to support the specification of the installed CT, in addition a full test report showing CT characteristics – checked against the standards. We recommend periodic retesting to maintain the validity of the CTs operation.

November 4, 2011 Posted by | Power Transformers, Relay Testing, Transformer Testing | , , , | Leave a comment

The Changing UK Power Distribution System – G59

The Electricity Power Sector in the UK has been changing over the past few years with the addition to the traditional large generating plants an increasing number of Distributed or Embedded Generation (DG) Systems with the push for low carbon renewable generation such as Solar, Water and especially Wind:-

Protection devices are necessary to comply with the national regulations for parallel connection of renewable energy systems to the Distribution Network – otherwise known as G59/2 Recommendations – has led to the introduction of specialist relays being developed.

G59/2 relays are designed to protect the DG from “Loss of Mains” – thus preventing unwanted interaction between the Generator and the Grid.

This could be caused by momentary disconnection of the DG from the grid leading to problems with synchronism, stability and – but most importantly – danger to personnel working on the grid in the area, where the DG could still be delivering power during the mains failure.

The G59/2 Relay provides this protection by monitoring the voltage, frequency and the rate of change of frequency (ROCOF) of the system and isolating the DG if these fall outside the G59/2 settings.

The Distribution Network Operators (DNO) now require that Low Voltage (LV) systems with an excess of 16A Per Phase require a Relay providing G59/2 protection and that the DNO witness the testing to prove compliance.

We can provide these tests on site using specialised, calibrated, 3 phase test equipment, and experienced test engineers throughout UK whether at an industrial or commercial installation – providing the DG operator with a test report to support their installed settings, additionally can also provide periodic retesting to maintain the validity of the relay settings.

If you would like to find out more about our services or just have a question about G59 relays, fire us an email to, or visit our website Why not take a look at our parent company Instrument Transformers Limited who manufacture instrument current and voltage transformers for utilities and electrical equipment manufacturers worldwide

July 28, 2011 Posted by | Relay Testing | , , , , , , , , , , , , | Leave a comment

New Product Line: 3PH, 120VA to 150kVA Transformers

ITL is proud to announce the launch of our comprehensive range of competitively priced, short lead time, 3 Phase Power Transformers from 120VA to 150kVA.

Designed to EN 60076-1 with insulation system to “Class E” (120 deg.C) or “Class F” (155 deg.C).

The entire range can be supplied either “Open” type with an aesthetically appealing golden polyester varnish or “Enclosed” in an IP rated sheet steel enclosure.

For more information ping with your full details.

July 26, 2011 Posted by | Power Transformers, Transformer Design | , , , , , , , , , | Leave a comment

Badly matched transformers give rise to spill currents :(

Phase Fault Stability

Current transformers which are well matched and operating below saturation, will deliver no current to the earth fault relay, since 3-phase currents sum to zero.

If however, the transformers are badly matched, a spill current will arise which will trip the relay. Similarly, current transformers must operate below the saturation region, since, in a 3 phase system, third harmonics in the secondary are additive through the relay thereby creating instability and erroneously tripping the earth fault relay.

I would like comments from switchgear / control panel manufacturers on how you handled spill current issues within your equipment.

To get our publication “Current Transformers for Protection of Electrical Plant” ping us a mail at or discover more about ITL and our product visit us at

July 22, 2011 Posted by | Protection Current Transformer | , , , , , , , , , | Leave a comment

Amendment to BS 7671 Wiring Regulations & Surge Protection

Amendment 1 of BS 7671:2008 17th Edition Wiring Regulations now includes a key new section (534) for protection against transient over-voltages using surge protection devices.

Over-voltages from atmospheric origin or electrical switching events can severely effect electrical installations and connected equipment.

The risks to life, buildings and electronics due to over-voltages are detailed within BS EN 62305 ‘Protection against lightning’ and can be reduced through the correct selection and installation of surge protection devices in accordance with Section 534. The new regulations were published on the 1 July 2011 and will come into effect on the 1 January 2012

I would be interested to hear comments and experience on the updated standard

July 13, 2011 Posted by | Health & Safety | , , , , | Leave a comment

Transformer Design Engineer

Want to work for a great company and make valued contributions to continued business growth?

We require an additional transformer design engineer whose role will be to liaise with customers and suppliers both within the UK and internationally relating to design, manufacture and sales of our custom designed products and providing advice and technical support to our customers.

Knowledge in the field of transformer design would be an advantage.

Candidates should preferably have experience in the Power Transmission / Distribution Sectors.

If you think you are up to the challenge and would like to know more about instrument transformers visit our website, and then reply in writing with CV to:

The Technical Director
Instrument Transformers Limited,
8 Lithgow Place, College Milton,
East Kilbride G74 1PW Scotland, United Kingdom.

Or email your CV, with covering letter to:

Strictly no agencies

July 9, 2011 Posted by | Design Engineer, Electrical Design Engineer, Transformer Design Engineer, Wanted | , | Leave a comment

Principles of Measurement Transformer Accuracy

Measuring instruments, such as ammeters, voltmeters, kilowatthour meters, etc , whether electromechanical or electronic, meet insuperable design problems if faced with the high voltages or high currents commonly used in power systems.

Furthermore, the range of currents employed throughout is such that it would not be practical to manufacture instruments on a mass production scale to meet the wide variety of current ranges required.

Current transformers are therefore used with the measuring instruments to:

(a) Isolate the instruments from the power circuits.

(b) Standardise the instruments, usually at 5 amps or 1 amp. The scale of the instrument (according to the CT ratio), then becomes the only nonstandard feature of the instrument.

Accuracy classes for various types of measurement are set out in the relevant IEEE(ANSI), CAN/CSA, AS or in our case BSEN /IEC 60044-1.

It will be seen that the class designation is an approximate measure of the accuracy, e g , Class 1 current transformers have ratio error within 1% of rated current. Phase difference is important when power measurements are involved, i.e. when using wattmeter’s, kilowatthour meters, VAr meters and Power Factor meters.

The table below details limits of error for current transformers for special applications and having a secondary current of 5A

Design Considerations

As in all transformers, errors arise due to a proportion of the primary input current being used to magnetise the core and not transferred to the secondary winding. The proportion of the primary current used for this purpose determines the amount of error.

The essence of good design of measuring current transformers is to ensure that the magnetising current is low enough to ensure that the error specified for the accuracy class is not exceeded. This is achieved by selecting suitable core materials and the appropriate crosssectional area of core. Frequently in measuring currents of 50A and upwards, it is convenient and technically sound for the primary winding of a CT to have one turn only.

In these most common cases the CT is supplied with a secondary winding only, the primary being the cable or busbar of the main conductor which is passed through the CT aperture in the case of ring CTs (i .e. single primary turn) it should be noted that the lower the rated primary current the more difficult it is (and the more expensive it is) to achieve a given accuracy.

Considering a core of certain fixed dimensions and magnetic materials with a secondary winding of say 200 turns (current ratio 200/1 turns ratio 1/200) and say it takes 2 amperes of the 200A primary current to magnetise the core, the error is therefore only 1% approximately. However considering a 50/1 CT with 50 secondary turns on the same core it still takes 2 amperes to magnetise to core. The error is then 4% approximately. To obtain a 1% accuracy on the 50/1 ring CT a much larger core and/or expensive core material is required.

To get this document in its entirety ping us a mail at

June 27, 2011 Posted by | Transformer Design | , | Leave a comment

A learning moment, what the Japanese Tsunami taught lean experts?

Questions were popping up after the massive tsunami hit the Japan on the reliability of the lean systems. Many people, including lean experts had their say on the subject. One of the common areas all the critiques comment on is the high vulnerability of the lean supply chain to a disaster. Even if the manufacturer doesn’t suffer, if the supplier does, then the manufacturer will have to eventually stop his production. Yes, there can be contingency plans in place. But still it is a bigger risk. Any risk for your supplier is a risk for you. Even a single day delay from one of your key suppliers, will eventually bring you in to a halt, and you don’t have to define a key supplier who supplies an expensive part, something as small and cheap as a special screw or nut which costs only few pence each, lose of supply has a huge knock on effect. This is what exactly happened after the Japanese tsunami. Whilst production is still not into full capacity in Toyota, and the full output is expected only in the early June. This is scary, regardless of whether you follow lean or not.

But the truth of the matter is, lean is not disaster proofed. It is vulnerable to any disaster just like any other system would be, or even sometimes little more. But let’s not forget the problems your system face if it runs the non-lean way.

When the system is not lean, you obviously will not be tightly coupled to your supply chain as you would do in a lean scenario. You may be able to go on for weeks, even if you do not get anything from your suppliers. What this means is you have this stock in-house. In case of a disaster, you will do much damage as your entire inventory will be destroyed. But one positive is, if you have stocks to work with, you will not be halted by the problems hit your supplying means. For an example, if your ports are damaged, you will not suffer, but only if you or your supplier is hit, you will suffer.

This goes to show, each system has its own share of risk, depending on the disaster they face. But the truth is, while we plan for the possibilities, we should work on probabilities. Not every day there will be a tsunami. But lean brings you savings, efficiencies and improvements every day. Probably, when you select the suppliers, you may go for a tight geographical grouping to avoid the associated risks. Or you may find a way to keep your operations going with some other means.

But the most important lesson taught by this event was the fact that nature is very powerful, and we must respect it.

June 2, 2011 Posted by | Lean Manufacturing | , , | Leave a comment

Eurotech, ITL country associate – Japan

ITL is proud to announce our new country associate in Japan.

Kawa Minami 1584-3
T 720-2124
Tel: (0081) 090 4107 2305

“As part of our associate expansion programme, Scott MacPherson and his team at Eurotech brings ITL an added dimension in the local Japanese market and we look forward to a long a prosperous relationship between our two companies” Paul Munro said.

January 6, 2011 Posted by | Country Agent | , , | Leave a comment

DOTIF 2010, what now?

Well 2010 is over and we have had a roller coaster year but all in all it is up. As we continue to reduce our lead times, it has become clearer that some suppliers drag their feet in focusing on sustained performance, but for those of you that have done a sterling job, you know who you are, well done.

Continued supplier improvement is one of our key tasks of 2011 and we shall be working hard with our valued supplier base to ensure we continue to build upon the 2010 success and exceed our levels of customer service.

January 5, 2011 Posted by | Lean Manufacturing, On Time Delivery | , | Leave a comment