All About Dry Type Transformer Protection

What are the types of transformer protection? Overheating protection Transformers become…

What are the types of transformer protection?

Overheating protection

Transformers become overheated from too much current passing through them and a breakdown in electrical wiring. The amount of overload and how long it can last varies depending on the type of transformer and its insulation.

Heavier loads can be supported briefly, but if prolonged, it can cause the insulation to degrade due to temperature exceeding a predetermined limit. In oil-cooled transformers, this limit is 95℃; beyond this point, the transformer’s life expectancy lessens and its wire insulation suffers. This is why overheating safeguards are so important.

transformer measurement device

Huge transformers contain oil or transformer winding temperature sensing instruments, which gauge oil or winding temperature, usually there are two strategies of measurement, one is labelled hot-spot measurement and the other is labelled top-oil measurement.

Overcurrent protection

unsupervise location of transformer

The overcurrent protection system is one of the oldest designed safety systems, the graded overcurrent system was made to safeguard against overcurrent conditions. Power distributors utilize this approach to detect faults with the help of IDMT relays, meaning the relays having:

1.Inverse characteristic, and

2.Minimum time of operation.

The capabilities of the IDMT relay is restricted. These sorts of relays have to be set 150% to 200% of the max rated current, otherwise, the relays will operate for emergency overload conditions. Therefore, these relays provide minor protection for faults inside the transformer tank. 

Differential Protection of Transformer

The Percentage Differential Protection is a highly widespread form of protection for power transformers and it offers the most comprehensive coverage. This type of protection is employed for power transformers that have an output rating exceeding 2 MVA.

The transformer is wired in a star formation on one end and a delta formation on the other. The current transformers (CTs) at the star side are connected with delta. And those at the delta side are connected as a star. Both of the neutral sides of the transformer are earthed.

The transformer consists of two coils, the active one and the restraining one. The restraining coil is responsible for generating a restraining force. While the active coil is used to create an operating force. The restraining coil is connected to the secondary winding of the current transformers. While the operating coil is linked to the same potential point of CT.

Earth Fault Protection (Restricted)

earth fault protection of transformer

When a breakdown occurs at the transformer bushing, an excessively large electric current can be generated. It is therefore essential to eradicate the fault swiftly.

The function of a particular safeguard apparatus should only encompass the area around the transformer; if any ground fault transpires in another place, then the relay allocated for that sector must activate and all other relays should remain as they are.

That is why it is known as a Restricted Earth Fault Protection Relay.

Buchholz (Gas Detection) Relay

The Buchholtz relay is installed between the primary transformer and the conservator tank. In case of a fault in the transformer, it detects the released gas with the aid of a float switch.

Commonly, there should not be any vapors inside the transformer. The majority of the gas is often known as dissolved gas and nine different kinds of gasses may be generated contingent on the defect state. On top of this device are two valves used to lower the accumulation of gas and to get a sample of it as well.

buchholz relay of transformer

When a fault condition occurs, we have sparks between the windings, or in between windings and the core. These small electrical discharges in the windings will heat the insulating oil. And the oil will break down, thus it produces gases, the severity of the breakdown, detects which glasses are created.

A substantial amount of energy will generate acetylene. And as is well known, the creation of acetylene requires a considerable quantity of energy. It ought to be kept in mind that any malfunction will give off gases. And the magnitude of gas can be determined by studying its quantity.

Over-fluxing protection

A transformer is made to be used at a set level of flux. If this amount of flux is gone beyond, the core gets filled to capacity, causing heating in the core which spreads rapidly to the other sections of the transformer leading to overheating of components.

Thus, over flux protection is necessary as it guards the transformer core. Over-flux events can happen from overvoltage or a decline in system frequency.

To shield the transformer from surpassing its flux threshold, an over-fluxing relay is employed. This mechanism takes into account the ratio of Voltage to Frequency with the objective of determining the level of flux density in the core. A sudden increase in voltage, caused by temporary imbalances in the power system, may lead to over fluxing. However, these peaks are short-lived and therefore it is not wise to trip off the transformer immediately.

The magnitude of the flux density is directly related to the ratio of voltage to frequency (V/f). If this rate surpasses 1, an electronic relay powered by a microcontroller will detect it. This mechanism measures voltage and frequency in real-time, then computes the rate and compares it against previously established values. The relay is programmed with inverse definite minimum time (IDMT) properties.

If it is necessary, the configuration can be done by hand. This way, the aim will still be accomplished without diminishing the safety against excessive fluxing. Now, we appreciate how essential it is to impede the transformer from becoming overloaded.

How To Commission The Dry Type Transformer?

Commissioning a dry type transformer is relatively straightforward. First, ensure the electrical winding ratio of the transformer is appropriate for the system. Then, transport it to the installation site. As they don’t require oil or other liquids, dry type transformers can be used indoors and are much less prone to dust contamination than their wet counterparts.

When installed, check that all connections are secure and that it can withstand the ambient temperature of the area in which it will be operating.

To complete commissioning, connect an AC power supply to the device and check that it operates as expected. Dry type transformers are reliable devices that should provide years of service if correctly installed and maintained.

SGB series dry type transformer

How To Maintain The Dry Type Transformer?

dry type transformer in factory

Maintaining a dry type transformer is essential to ensure that it operates correctly and safely. First, make sure to pay attention to the environment in which the transformer is installed; if it’s outdoors, keep it cool with shade or fans.

Also, be sure to remove any dust buildup on the device. Keeping the temperature and moisture levels regulated is also important for proper operation.

Regular maintenance should also be performed to ensure that all components are functioning properly. If any issues arise, they should be addressed immediately.

Additionally, consider upgrading the transformer if it’s been in use for many years to guarantee its effectiveness. By following these steps, you can help maintain your dry type transformer and ensure that it continues running smoothly for years to come.

Dry Type Transformer Protection

The dry-type transformer may utilize a variety of cases, contingent on the environmental conditions and protective needs. The IP20 safeguarding enclosure is typically employed to stop any solid foreign object larger than 12mm from entering, creating a security shield for live components. It can thwart little creatures (rats, snakes, cats, birds, etc.) from accessing and causing serious malfunctions like truncated circuit power failure.

If the transformer needs to be installed outdoors, the IP23 protective casing can be used. In addition to the above IP20 protection function, it can prevent water droplets from entering within 60° of the vertical line. However, the IP23 casing will reduce the cooling capacity of the transformer. When selecting, pay attention to the reduction of its operating capacity: the capacity is reduced by about 5%, and the capacity is reduced by about 10%.

The manufacturing facility routinely furnishes a formidable, attractive aluminum alloy shell. It can provide clients with varied levels of safeguard and protective shells of assorted elements (like aluminum alloy, steel sheeting etc.) according to their actual demands. In cases where the transformer is not already equipped with an exterior covering, it generally has IP00 protection.

well-protected dry type transformer

To sum it up, when the existing transformer is replaced with a new one in the design, energy efficiency and noise reduction can be expected.

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