For power transformers, the protection is to be provided usually against dangerous overloads and excessive temperature rise. Dangerous overloads may be due to external faults or the internal ones. External faults, however, are cleared by the relay system outside the transformer within the shortest possible time in order to avoid any danger to the transformer due to these faults. Hence [...]
The differential protection used for power transformers is based on Merz-Price circulating current principle. Such protection provides protection against internal phase-to-phase and phase-to-earth faults and is generally used for transformers of rating exceeding 2 MVA. This protection system as applied to power transformers is fundamentally the same as that for generators but with certain complicating features not encountered in the [...]
Summation devices are employed to compare the relaying quantities derived from the currents in the three phases of the primary circuit. The effectiveness of the comparison of the derived relaying quantities may be considered in terms of the effective ratio of the primary currents under comparison, such as at the two ends of a feeder. Summation devices are employed for [...]
The following points highlight the two main types of power transformers. The types are: 1. Current Transformers (CTs) 2. Potential Transformers (PTs). Type # 1. Current Transformers (CTs): Current transformers are connected in ac power circuits to feed the current coils of indicating and metering instruments (ammeters, wattmeter’s, and watt-hour meters) and protective relays. Thus the CTs broaden the limits [...]
Voltage Regulation is the way in which the secondary terminal voltage varies with the load depends upon load current, the internal impedance and the load power factor. The change in secondary terminal voltage from no-load to full-load, with primary voltage and frequency held constant, is termed the inherent regulation. The figure of merit which determines the voltage characteristic of a [...]
In this article we will discuss about the formula of emf equation. When an alternating (sinusoidal) voltage is applied to the primary winding of a transformer, an alternating (sinusoidal) flux, as shown is Fig. 10.2., is set up in the iron core which links both the windings (primary and secondary windings). Let ɸmax = Maximum value of flux in webers [...]
In a star-star or delta-delta 3-phase transformer there is no phase shift between the corresponding voltages of any phase to neutral on either side. However, a delta-connected winding is desirable in many power transformers for reasons of harmonic elimination. As such most of the power transformers are either star-delta or delta-star connected. In such transformers, even under normal operating condition, [...]
Transformer is a static machine which is used to transform electric power from one circuit to another without change in frequency. It may raise or lower the voltage in a circuit but with a corresponding decrease or increase in current. Thus transformer plays a vital role in power systems. Practically every transformer is provided with taps for ratio control, and [...]