How Thermography is Carried Out for the National Grid in New Zealand

Lyall Carson ABB Limited

ABSTRACT

This paper will provide an overview of how the annual thermographic survey program is carried out on substation equipment by ABB for Transpower, beginning with the planning process, through carrying out the survey using a FLIR PM595 camera and reporting with ThermaCAM reporter 7, then programming and carrying out the repair.

INTRODUCTION

Transpower owns the National Electrical Grid in New Zealand and takes the maintenance of its substations very seriously. ABB Limited (along with other contracting companies) carries out scheduled maintenance on substation and transmission lines for Transpower. One of the services ABB provides for Transpower is the annual thermography survey and repair program, to ensure Transpower’s continued commitment for KEEPING THE LIGHTS ON is achieved.

PLANNING

Surveys are best carried out in the winter months (June through August in New Zealand). This usually provides the coolest temperatures for carrying out the survey and highest loading on equipment. There are a few sites that differ from this rule i.e. Substations where the load is mainly rural and irrigation is the main source of power consumption. In these cases, summer time is the best time to complete the survey. Each year Transpower provide load graphs of the previous year’s energy consumption for each substation. Figure 1 is an example of one site. Using this information, ABB then plans a suitable time to carry out the survey.

Figure 1. Typical Substation Peak Load Graph

Where multiple bus configurations are available as in Figure 2, a request must be submitted to Transpower to carry out a bus change so that all equipment can be surveyed while carrying maximum available load.

Figure 2. Typical 110kV Double Bus Configuration

SURVEY

Documentation required for use on site:

1) Hazard Identification (identify hazards and stay safe)

2) Single Line Diagram (SLD) of substation layout

3) ITP (Inspection & Test Plan) Check list to ensure nothing is overlooked

4) Inspection Test Sheet Records all relevant information necessary for compiling the Thermographic

Report. Includes information such as ambient temperature, Wind speed, Weather condition, humidity,

Thermal Image number, Digital Image number, Equipment number.

On arrival at a substation, the thermographer first carries out hazard identification, and then records load information and status of all equipment before proceeding to survey all in-service equipment using a FLIR PM595 camera. Whenever a fault is discovered a thermal and digital photo image is recorded. All relevant information is then recorded on the check sheet.

On completion of the survey, a second check on equipment loading is carried out to ensure no significant increase/decrease of load has occurred, plus a check of all faults recorded to ensure there are none requiring immediate remedial action. Thus, if the fault was 50°C or higher above normal, then the thermographer would request the immediate release of this item of plant and call out a maintenance team to rectify the fault.

REPORTING

When the thermographer has completed his on-site surveys, he then returns to the office to compile the reports. Reports are generated using ThermaCAM reporter 7 software. ABB have developed a report template specifically for Transpower which complies with Transpower service specification publication TP.SS

02.07 (Ref 1). The main difference with the template is the calculation used for obtaining the peak load fault temperature when the fault was recorded during the time when load was less than peak load.

I stated above that we try and plan our surveys when the load is at its highest, but this is not always possible to achieve, so this calculation provides us with the information necessary. This corrected peak load temperature rise values provide excellent information about what to expect when the load goes up and can be used to help evaluate risk of going to higher loads – see figure 3.

Temperature rises due to resistive heating will increase significantly with load and need to be estimated. Historical references have indicated a square formulation to the increase in delta-T due to an increase in electrical load which our procedures are currently based on as shown in Figure 3. However, more recent studies indicate this is an overestimation of the temperature increase as it ignores heat transfer by radiation. For more details, see reference 2. We are evaluating the more recent results which give a lower temperature rise prediction than what we’re currently using.

Many factors need to be assessed when considering the severity of a suspected “hot spot”, not the least of these being the component material composition and the actual design temperatures for the conductors and equipment items. That is why it is necessary to estimate the maximum temperature rise at the annual peak load for suspected abnormal temperatures (figure 4).

Figure 3. Peak Load Assessment Formula Figure 4. Maximum Equipment Design Temperatures

Transpower uses a Maintenance Management System (MMS) for all scheduled/unscheduled maintenance to be carried out. Each item of plant has been allocated its own unique equipment number. This number is generated in Transpower’s MMS system. All information on each item is recorded in a database against the equipment number and is useful in retrieving information such as manufacturer details, type, serial number, load rating, age & estimated life expectancy etc.

Information on previous faults is also recorded in the report. This is used for trending purposes and is a useful tool in identifying inferior components that have a high failure rate and can be earmarked for nation wide replacement.2 copies of the report are generated – 1 for Transpower records and the second for the maintenance contractor (ABB).

The maintenance contractor then must program outages for the repairs to be carried out; based on the severity of the fault and the availability of existing outages. ABB are able to utilize any existing outages for thermal fault repairs where these opportunities exist. Otherwise, unscheduled outages are requested. These must be programmed at least 10 weeks in advance (unless faults are 35-50°C or above and the equipment is forced out immediately – see figure 5).

REPAIRS

The maintenance contractor is issued with the report on the faulty equipment, travels to site and proceeds to switch out the faulty equipment and makes it safe to work on (isolate and earth) He is then issued with an access permit to carry out the necessary repairs. The first action the maintainer must do is ductor (Digital Low Resistance Ohmmeter, see figure 6) the faulty component (disconnector contacts / CB bolted connection etc) and records these reading on his check sheet. A ductor is an instrument used for measuring resistance across the contacts. This is done by putting a current (10amps) and voltage across the equipment, then reading the resistance in micro ohms.

A typical contact requiring maintenance would have a reading greater than approx 300 micro ohms, up to 1 ohm. After maintenance the reading should be below 150 micro ohms. He can then proceed and carry out repairs. This may consist of cleaning and dressing contacts, replacing contacts, dismantling bolted connections, cleaning & dressing and re-assembling etc. On completing the repairs, he must then ductor the repaired component to confirm the repair was successful. A further scan with the PM595 when the equipment is returned to service can also be used to confirm the repair was successful if the ductor was unavailable. The access permit is cancelled and the equipment is returned to service.

The ductor results along with information on what was found and how the repair was carried out is then entered into the Transpower MMS system. This information is then open to Transpower staff and maintenance contractors nationwide and can be useful for trending purposes. The report can then be signed off as completed and filed for future reference.

Figure 5. Temperature Classification Analysis Chart Figure 6. 10amp Ductor

Transpower may also request thermography monitoring of significant faults where access to the equipment is not immediately achievable, such as high loadings etc.

TYPES OF FAULTS

We discover a wide variety of faults, some that could have enormous consequences and others that need only be monitored for further deterioration until an outage can be programmed. The following images are an example of some typical thermal anomalies found in Transpower’s substations.

Figure 7. Beaver Tail contacts heating on a 66kV Disconnector Figure 8. Photo of the same disconnector

Figure 9. 11kV to 33kV Transformer Radiators cooler – indicating possible blockage / oil flow valves turned off

NEW INSTALLATIONS

Transpower may also request thermography surveys of newly commissioned substations and equipment and extra surveys following major substation works.

INNOVATIONS

The importance of attending the Inframation conference for learning of new technology / innovations was highlighted by attending Inframation 2004, where I learnt of the IR windows available for installing in switchgear. The installation of IR windows gives the thermographer the ability to view connections / contacts that he has never before been able to access. This gives the thermographer the ability to identify potential faults within circuit breakers, transformer cable boxes etc. ABB is currently installing IR windows as a trial into a number of Transpower’s crucial transformers and circuit breakers to enable thermography to be carried out.

The costs benefits in identifying and rectifying faults before they fail are far more attractive than the cost of repairs after a failure has occurred. Figures 12 & 13 below are an excellent example. If the failing VT inside this Circuit Breaker had been identified with the use of a thermal imaging camera through an IR window, the repair could have only resulted in a 1 day outage and a VT replacement. However, after this Circuit Breaker blew up, there was an 8 day outage, plus the cost of sourcing and purchasing a replacement circuit breaker, voltage transformer, site construction work and labor costs for installing and testing.

ABB are committed to delivering the best service available to their customer, so are currently in the process of replacing their aging (but still good) P595 camera. With the advance in technology and recent introduction of a high resolution camera with a 640x480 detector, the logical choice of purchase is the camera that delivers the best image available. With a detector which delivers 307,200 pixels (as opposed to 76,800 on the PM595) ABB can deliver reports with images with up to 4 times better resolution than it has in the past. The thermographer will be able to identify faults easier and quicker, therefore improving quality of service to their customer.

SAFETY

ABB and Transpower are committed to safety, and together have made it mandatory for all staff to wear full PPE (personal protective equipment) when on a Transpower substation. This consists of hard hat, fire retardant full body cover, safety footwear, safety glasses and (where appropriate) gloves. To combat the problem of the thermographer wearing safety glasses while trying to look through the thermal camera view finder, we are purchasing a heads-up display color video viewer which I also discovered while attending the 2004 InfraMation conference. The heads-up unit is simply attached to your safety glasses and the cable is plugged into the camera. It then gives the thermographer the ability to simultaneously view his surroundings and live infrared video, keeping himself safe and increasing mobility.

SUMMARY

The thermographic survey program is a comprehensive tool that offers huge cost savings to Transpower by way of early fault detection and providing the ability to plan ahead to arrange outages for fault repairs. Using this program, we are able to reduce the number of unplanned outages and identify components that have a common failure record.

REFERENCES

1. Transpower Service Specification TP.SS 02.07. www.transpower.co.nz
2. Madding R.P., Leonard K. and Orlove G.L.; “Important measurements that support IR surveys in substations”; Proc. InfraMation; Vol. 3; pp. 19-33; Orlando, FL; 2002

ABB Limited Thermographic Survey of Transmission Equipment. www.abb.com/nz

ACKNOWLEDGEMENTS

The author acknowledges the support of ABB Limited and Transpower New Zealand Management staff for their assistance in the production of this work.

ABOUT THE AUTHOR

Lyall is a Level 1 thermographer and has been involved in infra red thermography for 11 years. He completed his Level 1 Theory & Practice of Infrared Thermography for Condition Monitoring with RMIT University in Melbourne, Australia in July 2002. He has had a major role in condition monitoring by way of annual thermographic inspections for most Transpower South Island sites in New Zealand. He has also built up a considerable clientele base of local power companies and factories in the upper South Island of New Zealand with condition monitoring using infrared.