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Air Circuit Breaker Maintenance

Primary Injection testing utilising a Megger ODEN AT primary injection tester to prove the Circuit Breaker protection unit and CT function. Sverker 780 proving the Circuit Breaker auxiliary under voltage release. TDC Aberdeen

Circuit Breaker Reset

Resetting a Circuit Breaker following a high current primary injection test. TDC Aberdeen

Protection Relay Test

Omicron 256+ protection relay test set and associated software during relay testing to ensure the relay operates within the manufacturers recommendations. TDC Aberdeen

Sverker 780 Setup

Setting up a Sverker 780 for secondary injection testing to confirm Circuit Breaker remote trip function. TDC Aberdeen

Maintenance Routine Thermal Image

Thermal image captured during a planned maintenance routine at client site. TDC Aberdeen

Transformer Operational Temperature

On completion of control panel modifications, a thermal sweep confirms the Transformer operational temperature and connection security. TDC Aberdeen

Thermal Analysis

During a planned maintenance routine, a loose connection is discovered, during thermal analysis, on a capacitor bank. TDC Aberdeen

Rotating Machine Thermal Survey

Rotating Machine Thermal Survey performed with a Flir P640 camera to ensure the machines remain within specification and hazardous area T rating. TDC Aberdeen

Secondary Injection Testing

OMICRON 256 plus during set up for secondary injection testing of a three-phase relay. Test Universe software displaying the test parameters. TDC Aberdeen

Trip Test on Circuit Breaker

Performing a trip test on a 3-phase circuit breaker using the Megger ODEN AT primary injection test set. TDC Aberdeen

TDC's Electrical Condition Monitoring Services are designed to provide the end user with the information to predict when preventive maintenance routines should be carried out.

Below you will find a menu highlighting all of our main services relating to Condition Monitoring.

CM - Sub Divisions
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In the world of power engineering the cost of equipment failure can have a catastrophic effect on your business. Profit lost during the downtime, replacement and installation cost, environmental impact, the cost of the failed equipment disposal as well as the safety risk to operators during the actual failure can have a severe impact on a company’s operation. Most failures are often the result of poor maintenance schedules, ageing equipment or unexpected failures due to inadequate knowledge of the equipment condition.

Predictive maintenance techniques provided by TDC Electrical Condition Monitoring Services are designed to provide cost savings in relation to preventive maintenance routines. It provides the end user with the information to predict when preventive maintenance routines should be performed based on the condition of the equipment and therefore reduce the requirement for time-based maintenance routines.  

Monitoring of equipment and subsequent analysis of the data provides information on the status of the equipment and determines the best possible route for future maintenance or replacement. Thus, allowing the end user to plan the maintenance schedule especially on critical equipment that requires minimum downtime or long lead time replacement equipment.

The continuing expansion of the Condition Monitoring Division at TDC has resulted in an increase in the services provided in line with the growth in Predictive Maintenance Techniques.



Partial Discharges can be described as a localised breakdown of the insulation under High Voltage (HV) stress. These electrical discharges normally do not completely bridge the gap between conductors. However, if these discharges are left undetected then they continue to erode the machine insulation leading to a catastrophic failure of the machine. The various types of discharges related to HV machines include: -

  • Internal discharge 

  • Surface discharge 

  • Corona discharge

  • End winding discharge

Partial Discharge is second only to bearing faults as the most common failure mechanism in HV machines. Partial Discharge and the subsequent insulation failure is a result of a combination of various factors that mainly include Electrical, Mechanical, Environmental and Thermal stresses. The detected problems relate to: -

  • Internal voids within the insulation

  • Loose wedges

  • Coil movement within the stator slot

  • End winding contamination

  • Insulation damage

  • Ageing insulation

  • Delamination

The TDC Partial Discharge system is suitable for generators and motors above 4kV. The system is non-intrusive and the test is performed by our field engineers under normal running conditions. The data gathered during the test is analysed by our specialists using our propriety PD analysis tools that include statistical signal processing and pattern recognition. The diagnosis provided regarding the stator winding insulation condition includes: - 

  • Severity of the fault

  • Location of the fault

  • Recommendation for re-survey

  • Recommendation on replacement / repair


Contact us for more information on our HV Machine Partial Discharge (PD) Analysis.




Motor Current Signature Analysis is a method that has been reliably used for rotor fault detection in AC Induction motors.

The technique is specific to rotor faults such as: - 

  • Broken bars 

  • High resistance joints

  • Cracked end rings

  • Eccentricity. 

AC motors are the main prime movers in industry and have been proven to be reliable under the normal operating conditions. When used outside of normal operation or in the presence of excessive thermal and mechanical stress the rotor failure can develop rapidly. The various factors that contribute to increased thermal and mechanical stresses are:

  • Direct on Line start

  • Manufacturing defects

  • Heavy duty cycles

  • Repeated starts

  • Reciprocating loads

The above factors contribute towards fault progression and may result into a motor failure due to:


  • Increased Heat

  • Rotor imbalance

  • Stator rub

  • Broken bars coming into contact with the stator

  • Material separating from the bars and making contact with the stator.

The MCSA technique is only suitable for AC induction motors above 40kW with a minimum 60% load.  The process entails data collection and analysis to determine the status of the rotor.  The current signal is sampled via a clamp-on CT on the primary or secondary circuits of the motor. The data is then transformed into frequency domain by Fast Fourier Transformation that allows the identification of the rotor fault frequencies and also determine the fault severity.

Contact us for more information on our Motor Current Signature Analysis (MCSA).



Thermographic surveys have become an indispensable tool in the Electrical / Mechanical field to find faults and abnormal operating conditions. This is prudent for employee’s safety from the risk of fire / equipment failure and the expense of downtime of production facilities through power or mechanical failure.

Electrical Thermographic Surveys of switchboards, transformers, cabling and individual electrical components is essential for the early detection of faults across a wide range of industries. The identification of   temperature changes by regular inspection and analysis allows preventive maintenance to be performed before plant failure. These non-invasive surveys identify faults such as: -

  • Loose connections

  • Load related problems (overload and imbalance)

  • Thermal breakdown of ageing components. 

  • Premature component failing due to increased thermal stress

  • Temperature exceeding hazardous area temperature ratings. 

Mechanical Thermographic Surveys of Generators, Motors, Pumps, Vessel levels and Pipework provides a thermal record of the equipment. This can be utilised as a single survey relating to specific hot spots or carried forward to trend the temperature changes over time.  Faults associate with temperature rise include: -


  • High Generator/Motor/Pump operating temperatures

  • Bearing breakdown

  • Misalignment (pulleys, shafts)

  • Pipe blockages

  • Vessel levels

  • Insulation breakdown

The Field Engineers at TDC have up to 25 years individual experience in Thermography and up to ITC Level II certification. 


Contact us for more information on our Thermography Services.




Secondary Injection Testing is carried out to determine the correct operation of circuits connected to the secondary side of the control circuit transformers. These include Protection relays, metering and low voltage devices such as shunt trips, sensors and transducers. The focus of Secondary Injection Testing relates to Protection relay testing and Circuit Breaker trip tests. 

Protection Relay Testing is performed to ensure that the trip functions of a relay under various fault conditions are maintained within the manufacturers specification. Field Engineers at TDC have a wide range of experience in protection relay testing that include models from early mechanical devices to the modern solid state multi-function relays. The testing of single phase and three phase relays include: - 

  • Trip Timing checks as per settings 

  • Correct operation of Auxiliary contacts

  • Alarm functions

  • Polarity checks

  • Physical conditions


We have an extensive range of in-house test equipment within the division with additional equipment available via our Test Equipment Hire Division. These include OMICRON 3 phase test units & Sverker single phase units.  Each unit is accompanied by a full Relay toolkit including specific manufacturer’s test blocks, test probes, resistors, multi-meters and various hand tools.

Circuit Breaker secondary injection testing is an alternative to the standard Primary Injection Testing. Secondary injection testing can be carried out if Primary Injection is not possible or only the trip function requires to be tested. These tests prove the operation of the trip units are within the manufacturers trip time curves.

Modern Circuit Breakers have test points located in the trip circuit to allow for manufacturer specific tests sets to be used to prove the trip circuits. These units simulate the trip circuit currents to ensure the trip units operate as intended. Older Circuit breaker designs can be the open wiring design type where the trip circuits are accessible and standard secondary injection test sets can be used.   


Contact us for more information on our Secondary Injection Testing Services.



Primary Injection Testing is carried out to verify the protection schemes operates within the manufacturers specifications throughout the complete circuit.  Unlike Secondary Injection Testing this proves the whole circuit rather than individual protection components. This is normally a high current test to prove that the system can withstand the stress associated with the fault currents of the equipment. The injected currents are in the range of 2-10 times the breaker current rating.  

Primary Injection Testing is most commonly used to prove: -

  • Circuit Breaker trip unit

  • Correct CT operation

  • Correct CT ratio and polarity

  • Primary and secondary circuit wiring

  • Auxiliary trip circuits (under voltage, shunt trips) and remote operation

In house equipment includes 3-phase Programma ODEN systems with capabilities of up to 20kA. The full test kit also contains various auxiliary equipment like AC/DC power supplies for checking various coil types, an assortment of adapters to couple the test set with the breaker and various cable sizes to accommodate the testing of a wide range of breakers. 


Contact us for more information on our Primary Injection Testing Services.



The majority of faults in HV switchboards are related to mechanical faults (38%) and discharge faults (44%). The single most disruptive failure relates to discharge which constitutes up to 85% of all failures.  These failures result in power outages, equipment failures and protection failures which can lead to catastrophic failure / fire.

Failures due to discharge include: -

  • Design defects

  • Insulation defects such as voids within the insulation

  • Mechanical breakdown or damage to insulation

  • Contamination

TDC provides switchboard Partial Discharge (PD) monitoring services in alliance with EA Technology. PD trained TDC field engineers utilise the latest PD test equipment to perform the surveys Onshore/Offshore/Overseas with the data returned for comprehensive analysis. The results from this analysis provides the key information for maintenance intervention. 
The PD associated with HV switchboards includes: -

  • Surface Discharge

  • Cavity Discharge (internal)

  • Delamination Discharge

  • Treeing

The techniques used for PD detection include Transient Earth Voltage (TEV) and Ultrasonic. 

TEV is primarily associated with high level internal discharge to earth within the 2-80MHz range. TEV are electromagnetic pulses that travel through the switchboard and over the surface of the switchboard. These pulses are detected via magnetically mounted capacitive probes attached to the switchgear. 

Ultrasonic instruments are associated with surface discharge in the region of 40kHz range. The most sensitive ultrasonic signals are airborne and requires a direct line of sight to the discharge site. Ultrasonic contact probes can be utilised where switchboards are of a sealed chamber construction.

These techniques are suitable for switchboards from 3.3kV and above, where the surveys can improve asset performance with fewer outages, provide a financial benefit of reduced preventative maintenance and increased safety.



Contact us for more information on our HV Switchboard Partial Discharge Analysis services.

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