TERTIARY WINDING OF TRANSFORMER - THREE PHASE TRANSFORMER

Electrical Transformer is a static device which transform electrical energy from one electrical circuit to another electrical circuit without any direct connection. It is also used for electrical power transmission (Step-Up) and distribution the electrical power (Step-Down) and Special purposes. Commonly we know that there are two windings in transformer, The primary winding and the secondary winding. The primary winding is used for input (not fixed) and the secondary winding is used for the output whether it depend upon the situation and requirement. Now there is a question asked an engineer from our Facebook group (Facebook-Group) that what is Tertiary winding in the three phase transformer, the advantages and disadvantages of tertiary winding.

Working Principle Of Transformer

The working principle of transformer is totally depends upon the Faraday's Law of mutual induction.
Faraday's Law of Mutual Induction is:

"Rate of change of flux linkage with respect to time is directly proportional to the induced EMF in a conductor or a coil."

As you all know well about the transformer working, I will try not to discuss here again. but the main constructional parts of the transformer I share below.

Main Constructional Parts of Transformer

There are following main part of transformer in construction.

• Primary Winding
• Secondary Winding
• Magnetic Core of transformer

Now What is Primary winding? The Primary winding of transformer which produce magnetic flux when it is connected to electrical source. And What is the secondary winding? The Secondary winding of transformer is the flux, produce by primary winding, passes through the core will link with the secondary winding. This is also wound on the core of transformer and gives the desired output of the transformer. And the magnetic core of transformer is the magnetic flux produced by the primary winding that will pass through with low reluctance path linked with secondary winding and create a close magnetic circuit in the transformer.

tertiary winding how electrical blog

Tertiary Winding of Three Phase Transformer

As we already discuss, there are two windings in the transformer. There is another additional winding we used named "Tertiary Winding". This winding is used in the high rating transformer for the purposes below mentioned.  Because of this third winding, the transformer with tertiary winding is also known as three winding transformer.

Advantages of Tertiary Winding in three phase transformer

There are following advantages of tertiary phase winding.

1. Tertiary Winding reduces the unbalancing in the primary due to unbalancing in three phase load.
2. Tertiary Winding redistributes the flow of fault current.
3. Sometime Tertiary Winding is required to supply an auxiliary load in different voltage level in addition to its main secondary load. This secondary load can be taken from tertiary winding of three winding transformer.
4. As the tertiary winding is connected in delta formation in 3 winding transformer, it assists in limitation of fault current in the event of a short circuit from line to neutral.

Rating of Tertiary Winding.

Rating of tertiary winding depends upon its use. If it has to supply additional load, its winding cross - section and design philosophy is decided as per load, and three phase dead short circuit on its terminal with power flow from both sides of HV & MV. In case it is to be provided for stabilizing purpose only, its cross - section and design has to be decided from thermal and mechanical consideration for the short duration fault currents during various fault conditions single line to ground fault being the most onerous.

Read More

OBJECTIVES OF POWER SYSTEM - ELECTRICAL POWER SYSTEM

The objective of power system control is to maintained continuous electric supply of acceptable quality by taking suitable measures against the various disturbances that occur in the system.

These disturbances can be classified into two major heads, namely, small-scale disturbances and large scale disturbances.

Small Scale Disturbances

Small scale disturbances comprise slowly varying small magnitude changes occurring in the active and reactive demands of the system.

The small scale disturbances can be overcome by regulating controls using  governors and exciter.

Large Scale Disturbances

The large scale disturbances can only be overcome by proper planning and adopting emergency switching control.

Large scale disturbances are sudden large magnitude changes in system operating conditions such as faults on transmission network, tripping of a large generating unit or sudden connection or removal of large blocks of demand.

Objectives of Power system control

To meet continually changing load demand

Adequate “spinning” power reserve

Minimum cost of energy

Minimum environmental pollution

The “quality” of power supply

                (a) constancy of frequency

                (b) constancy of voltage; and

                    (c) level of reliability

Frequency Regulation

System frequency, must remain within its operational range

                         f _min < f(t)  <  f _max

                      49.5 Hz < f(t)  <  50.5 Hz

Voltage Regulation

Bus voltages must remain within their operational limits

                         V _min < V(t)  < V _max

                      0.95 pu < V(t)  < 1.05 pu

Quality is normally described by means of an accepted voltages profile (level and amount of flicker) and frequency (set point with a narrow band and a threshold for the time delay) of the delivered electric power.

Security is much more difficult to describe in quantitative terms. There are normally certain rules in utilities and power pools concerning power system balance, network operation etc. In order to successfully take care of care of some predefined disturbances.

Economy consists of two parts: The investment part of apparatus, control system and so on, and the running cost for the while power system.

To keep the objectives on reasonable level it is a must today to take advanced control systems into service.

Read More

POWER SYSTEM CONTROL - ELECTRICAL POWER SYSTEM

The concept of control is fundamental to the functioning to the proper functioning of any system.

Irrespective of whether it is an engineering system or an economic system or a social system, it is essential to exert some kind of control, such as quality control, inventory control, or population control, to achieve certain objectives like better quality of output or better economics, etc.

Power system control has gone through a lot of changes over the past three decades. Beginnings with simple governor control at the machine level, it is now grown into a sophisticated multilevel control needing, a real-time computers process, and system-wide instrumentation.

IMPORTANCE OF CONTROL SYSTEM ELECTRICAL POWER.

1.  Stability and Security must be maintained.

2.  Protection of system from any damage.

3.  System must operate Efficiently and Economical.

4.  All system functions and major equipment's  are monitored,  evaluated and controlled.

5.  Future demand prediction and establish favorable  trade conditions between utilities.

The control objective are dependent on the operating state of the power system. Under normal conditions, the control objective is to operate as efficiently as possible with  voltages and frequency close to nominal values. When an abnormal conditions develops new objectives must be meet to restore the system to normal operation

The control system has several measuring instruments and actuators, it is natural to group these together on a control panel or mimic board. In this way the operator can obtain an image of the status of the process from one or a few locations.

For geographically widespread processes these control centers are located in buildings separate from the process plant.

Traditional control rooms consist of a mimic board which is a schematic model of the process and or several control disks, and displaying the state of process, e.g. voltages, power flow and breaker status.

The size of mimic board is directly proportional to the size and complexity of the monitored process.

The electrical power process is to continual change new lines stations etc are constantly added.

Consequently the mimic board becomes more complex.

It is from this base that the highly flexible control centre systems of today evolved.

Many modern control rooms that relay on VDU display techniques.

Read More

LOAD FORECASTING - ELECTRICAL POWER SYSTEM

Load forecasting is vitally important for the electric industry in the deregulated economy. It has many applications including energy purchasing and generation, load switching, contract evaluation, and infrastructure development.

Accurate models for electric power load forecasting are essential to the operation and planning of a utility company. Load forecasting helps an electric utility to make important decisions including decisions on purchasing and generating electric power, load switching, and infrastructure development. Load forecasts are extremely important for energy suppliers,

ISOs, financial institutions, and other participants in electric energy generation, transmission, distribution, and markets.

Load forecasts can be divided into three categories:

1. Factors for accurate forecasts 
2. Weather influence
3. Time factors

Weather Influence

Electric load has an obvious correlation to weather.  The most important variables  responsible in load changes are:

• Dry and wet bulb temperature
• Dew point
• Humidity

Wind Speed / Wind Direction

• Sky Cover
• Sunshine
• Time factors

In the forecasting model, we should also  consider time factors such as:

The day of the week

The hour of the day

Holidays

Read More

GENERATION OF HIGH VOLTAGES | AC AND DC VOLTAGE GENERATION

HVDC is used for testing HVAC cables of long lengths as these have very large capacitance and would  require very large values of currents if tested on HVAC voltages. Even though D.C. tests on A.C cables is convenient and economical, these suffer from the fact that the stress distribution within the insulating material is different from the normal operating condition.

In industry it is being used for  electrostatic precipitation of ashing in thermal power plants, electrostatic painting, cement industry, communication systems etc. HVDC is also being used extensively in physics for particle acceleration  and in medical equipment's (X-Rays).

The most efficient method of generating high D.C. voltages is through the process of rectification employing voltage multiplier circuits. Electrostatic generators have also been used for generating

high D.C. voltages.

According to IEEE standards 4-1978, the value of a direct test voltage is defined by its arithmetic mean value   and is expressed mathematically as 

where T  is the  time period  of the voltage wave having a frequency f = 1/ T.  Test voltages generated using rectifiers are never constant in magnitude. These deviate from the mean value periodically and this  deviation is known as  ripple . The magnitude of the ripple voltage denoted by  δV  is defined as half the difference between the maximum and minimum values of voltage  i.e.,

and ripple factor is defined as the ratio of ripple magnitude to the mean value  V d

  i.e.,   δV/V d .  The  test voltages should not have ripple factor more than 5% or as specified in a specific standard for a particu-lar equipment as the requirement on voltage shape may differ for different applications.

Read More

WHY AC SYSTEM ARE PREFERRED OVER DC

We (Usually all over the world), In all the countries, We use AC voltage for consuming and for use electricity. Why not DC voltages?
It may ask you in an interview so it's better to know it first.
There are some factors for using AC rather than DC.

• From powerhouse/power plant, we produce AC voltages so it's better to use AC rather than convert it from AC to DC (because there is extra no benefit to using DC). We need to change transformers, breakers and other devices that we are using at the powerhouse.
• It is easy to maintain AC voltages and step up & step down AC voltages as compared to DC.
• The cost of power-plant is much lower than the DC generation plant (transformers, circuit breakers etc).

Read More