Electrical Power & Protection


Common power quality factors affecting transformers

May 2024 Electrical Power & Protection

Commercial and industrial buildings commonly have a 208/120 V transformer in a delta-wye configuration to feed receptacles. Single-phase, non-linear loads connected to the receptacles produce triple harmonics, which add up in the neutral. When this neutral current reaches the transformer, it is reflected into the delta primary winding, which causes overheating and transformer failures.

Another transformer problem results from core loss and copper loss. Transformers are typically rated for a 60 Hz phase current load only. Higher frequency harmonic currents cause increased core loss due to eddy currents and hysteresis, resulting in more heating than would occur at the same 60 Hz current.

Transformers supplying nonlinear loads should be checked periodically to verify operation within acceptable limits. Transformers are also critical to the integrity of the grounding system.

The proper grounding of the transformer is critical. There are several solutions for transformer-related power quality (PQ) problems:

Separately derived systems (SDS)

The distribution transformer is the supply for a separately derived system (SDS). The key idea is that the secondary transformer is the new power source for all its downstream loads. This is a powerful concept in developing a PQ distribution system. The SDS accomplishes several important objectives, all beneficial for PQ:

• It establishes a new voltage reference.

• It lowers source impedance by decreasing, sometimes drastically, the distance between the load and the source.

• It achieves isolation.

• A new ground reference is established.

K-rated transformers

Harmonics cause heat in transformers at a greater rate than the equivalent fundamental currents. This is because of their higher frequency. There are three heating effects in transformers that increase with frequency: hysteresis, eddy currents and skin effect.

Application issues with K-factor transformers

K-rated transformers have been widely applied, but there are specific issues with them. Many consultants do not see the need to use transformers with a rating higher than K-13, although K-20 and higher might be supplied as part of an integrated power distribution unit (PDU).

Derating standard transformers

Some facilities managers use a 50% derating as a rule of thumb for their transformers serving single-phase, predominantly nonlinear loads. This means that a 150 kVA transformer would only supply 75 kVA of load. The derating curve, taken from IEEE 1100-1992 (Emerald Book), shows that a transformer, with 60% of its loads consisting of switched-mode power supplies, should be derated by 50%.

Forced air cooling

If heat is the problem, cooling is the solution. Break out the fan, turn it on the transformer, and use forced air cooling. Some experienced hands figure that’s worth 20-30 % on the upside.

Product: https://bit.ly/4aAJ2R7


Credit(s)



Share this article:
Share via emailShare via LinkedInPrint this page

Further reading:

Measuring and analysing PV circuit performance
Comtest Electrical Power & Protection
Regardless of the test method, you must know the plane of array irradiance and cell temperature to evaluate PV circuit performance. Proper sensor types and test methods like the Fluke Solmetric PVA 15i-V curve tracer should be used for reliable results.

Read more...
Enabling Africa’s solar potential – lighting the way with technology
Electrical Power & Protection
As the global population continues to grow, energy demand also rises. ABB can help bridge the gap throughout the renewable power value chain, including consulting, generation, storage, transmission, monitoring, control and optimisation.

Read more...
AES and the great decarbonisation debate
Electrical Power & Protection
Although many manufacturing and industrial companies have objectives to reduce the use of fossil fuels, there are not yet any silver bullets in the green fuel space. Supply and logistics constraints, high costs and technological limitations are just some of the challenges encountered by AES, as they assist an increasing number of clients to investigate the use of more environmentally sustainable, lower carbon fuel alternatives, thereby obviating the requirement to pay

Read more...
Distributed servo drive system with extended voltage range and additional braking option
Beckhoff Automation Electrical Power & Protection
Beckhoff’s AMP8620 supply module and AMP8805 distribution module are now also available with an extended voltage range for the AMP8000 distributed servo drive system.

Read more...
Data acquisition modules
Vepac Electronics Electrical Power & Protection
The D1200 current input modules from Vepac include one discrete digital input and two open-collector digital outputs for monitoring On/Off signals or controlling solid-state relays and annunciators. The digital outputs can also be programmed to operate as HI/LO alarm outputs based on the input current level.

Read more...
Grid management systems are the backbone of modern T&D networks
ACTOM Electrical Machines Electrical Power & Protection
Grid management systems are the linchpin of modern transmission and distribution networks, ensuring their reliable and efficient operation.

Read more...
Electrical power solutions from TRAFO
Electrical Power & Protection
Having rapidly carved a niche in dry-type transformer applications in Africa, Trafo Power Solutions has steadily grown its offerings, and now sees a future as a leading provider of electrical power solutions. ...

Read more...
Boiler update at food processing plant transforms production process
Electrical Power & Protection
The replacement of 78 year-old boilers at a Western Cape food processing plant by Associated Energy Services has not only proven to be a worthwhile investment for the client, but has transformed its entire production process.

Read more...
Three financing trends driving clean energy in the Global South
Schneider Electric South Africa Electrical Power & Protection
The Global South is at a critical juncture in its energy transition, grappling with challenges that demand immediate action. To finance its energy targets, the World Economic Forum’s Network to Mobilise Clean Energy Investment in emerging markets and developing economies has developed a playbook of over 100 financing mechanisms and de-risking tools that have successfully helped narrow the clean energy financing gap in emerging and developing economies.

Read more...
New generation low power frequency inverters
Bearing Man Group t/a BMG Electrical Power & Protection
New to BMG’s electromechanical range are energy-efficient Synergy PI150 series frequency inverters, which have been designed for efficient use in many applications.

Read more...