What is Transformer Vector Groups ?

 The transformer vector group shows the phase difference between the primary and secondary sides of the transformer. It also determines the high voltage and low voltage windings arrangement of three-phase transformers. The three-phase transformer is connected in various ways. On the basis of connection, the vector group of the transformer is determined.

A three-phase transformer is divided into four main groups according to the phase difference between the corresponding line voltage on the high voltage side and the low voltage sides. The phase difference is the angle by which the low voltage line lags the high line voltage, and is measured in units of 30° in a clockwise direction. These groups are

Group number 1 – no phase displacement

Group number 2 – 180° phase displacement.

Group number 3 – (-30°) phase displacement.

Group number 4 – (+ 30°) phase displacement.

The connection Y d 11 gives the following information – Y indicates that the high voltage is connected to star and d indicates the low voltage is connected in delta. The 11 indicates that the low line voltage lag, high line voltage by 11 Χ 30° = 330° measured from higher voltage phasor in a clockwise direction.

The phasor differences can also be measured by using the clock methods. Consider the minute hand of the clock shown the high voltage and the low voltage winding is represented by the hour hand. The angle of 30° is the angle between two adjacent figures on the clock dial and is taken as the unit of dial shift.

When the hour hand of the clock is at 12, then the phase displacement is zero. When the hour hand is at 1 then the phase shift -30° degree. At 6 the phase shift is 6 Χ 30º = 180º. Similarly, when the hour hand is at 11 the phase shift is 11 Χ 30º  = 330º.

The number 0, 6, 1, and 11 in the group reference number indicates the primary to secondary phase shift regarding the hours of the clock. The connection designated by D y 11 is the delta-star transformer in which the low voltage line phasor is at 11 and is a phase advanced of +30° on the corresponding line voltage on the high voltage side.

Note: The only transformer in the same group may be connected in parallel. For example, a star-star, 3-phase transformers can be parallel with another three-phase transformer whose windings are either connected in Y-Y or ∆-∆. The ∆-∆ transformer cannot be parallel with Y-∆ transformer.

Difference Between Heat and Temperature

 

Comparison Chart

Basis for Comparison	Heat	Temperature
Basic	A form of energy	Measurement of thermal energy in a substance.
Symbolically represented as	Q	T
Defined as	Ability to do work.	Measures the amount of heat.
SI unit	Joule	Kelvin
Other measuring units	Calories	Fahrenheit, Celsius
Depends on	Mass, type of particle, speed of the particle.	Only on average molecular motion.
Measured by	Calorimeter (using principle of calorimetry)	Thermometer
Signifies	Total potential and kinetic energy of the substance	The average kinetic energy of the molecules of the substance.
Measurement	Product of no. of molecules and energy possessed by each molecule.	The speed of molecular motion in a substance signifies the level of temperature.

Difference Between RTD and Thermocouple

 

Comparison Chart

Basis for Comparison	RTD	Thermocouple
Operating Principle	Temperature changes with a change in resistance.	Temperature changes with change in emf generated.
Response time	1 – 50s	0.1 – 10s
Cost	High	Low
Operating range	-200 to 600°C	-200 to 2000°C
Physical size	Large	Comparatively small
Sensitivity	Low	Quite high
Accuracy	More	Less
Self-heating	Exist	Not Exist
Stability	More	Comparatively less
Output	Linear	Non-linear
Applications	Used to measure engine temperature along with the temperature of amplifier and oil temperature sensor, etc.	Measures the temperature of chemical and petroleum plants and detects the temperature of metals and aluminum for industrial purposes.