Minimization of Power Loss & Improvement in Voltage Profile of 11kV Feeder by Different Techniques

India’s power sector is a ‘Dripping Vessel’ and the logical thing to do would be to fix the bucket properly rather than persistently emphasize shortage of power. China is way ahead of to meet with increase in demand of electricity, the increase in production and reduction in losses has been equally given importance. The distribution reforms are identified as the main area to improve gap between supply and demand.

The distribution system plays an important role in any electric power system and requires a detail analysis of various types of losses occurring in a distribution system and methods / techniques are required to be developed for reducing the same. The losses occurring in a distribution system can be classified into following three categories.

• Technical Loss
• Non-Technical Loss
• Administrative Loss.

Thus in this article it is clear that distribution sector is an area where by applying the different techniques the efficiency, voltage profile can be improved. In this article the following techniques are applied for loss reduction and improvement of voltage profile.

• By restructuring of transformer or relocation of transformer,
• By VAr compensation incorporation at different busses and
• By changing the conductor size / type of feeder. In order to bridge the gap between demand and supply. The Technical and economic feasibility is also conducted in this work.

Fig. 1: Punjab last three year energy available & consumption (Source: psebea.org)

Restructuring Parameters

In order to restructure the Feeder – 11kV of the Sub Station we need to achieve the following objectives.

• Transformer loading- Under normal conditions a distribution transformer is not loaded more than 50%. Transformer will generally have an overloading capacity of 200% (double their rating) but these conditions are avoided by load shedding. As per standards [IS-6600] or [IEEE Guide for loading] transformer loading is kept at 50% loading, with 3-4% loss.
• Transformer relocation/ restructured- Also known as Distribution Transformer (DTR) relocation. In such cases either the transformer of lower capacity will be replaced by a higher one or may be replaced by the desired one. For instance if the load demand is 60 kW it is feasible to put a 100 kVA transformer and not 200 kVA because the balance 100 kVA will not be used.
• VAr compensation- Reactive power neither consumes nor supplies energy. It is useful to visualize the impact of various devices on the reactive power of a power system as follows:

Sources of reactive power which raise voltage:

• Generators
• Capacitors
• Lightly loaded transmission lines due to the capacitive charging effect.

Sinks of reactive power which lower voltage:

• Inductors;
• Transformers;
• Most heavily loaded transmission lines due to the I2 *XL effect;
• Most customer load (due to the presence of induction motors and the supply to other electric fields).

Changing the conductor size / type of feeder – Changing the feeder effectively reduces the loading on the line/cable. This due to the reason is the capacity of the line and Impedance of the cable. A Cable which can carry 4 MVA can carry 4.8 MVA depending 20% growth rate in the load [IEEE Cable 57.91] or [IEC 60853] or [IEC-60287]. More the conductor size less is the impedance and better power flow with less line losses or voltage drops.

Improving Voltage profile – Voltage profile will be improved by the following methods:

• VAR Compensation
• Changing the Conductor for better power flow / loading.

Fig. 2: Punjab last three year % Energy inputs and T & D losses (Source: psebea.org)

Modeling of a Feeder

One of the most common computational procedures used in power system analysis is load flow study. The planning, design and operation of power systems requires such calculations to analyse the steady-state transient performance of the power system under various operating conditions and to study the effects of changes in equipment configuration. A load flow calculation determines the state of power system for a given load and generation schedules. A number of operating procedures can be analysed, including contingency conditions, such as the loss of a generator, a transformer, a transmission line, or a load. These studies will alert the user to conditions that may cause equipment overloads or poor voltage levels. Load flow studies can be used to determine the optimum size and location of capacitors for power factor improvement.

Basic features of the feeder include:

Table 1: Basic Features of 11kV Feeder

This shows the conversion of the above data which is taken from public utility company into a simulated diagram which has been obtained with the application of MiPower software. This helps in computing the load flow analysis and actual losses at the feeder level in a more scientific accurate manner.

Fig. 3: Analysis of results

Application of the VAr compensation, better choice of feeder type and transformer loading are the best techniques for voltage profiling. Real power loss is found to be minimum by the use of above features. Following is the outcome of the application of transformer loading (A), VAr compensation (B) and changing the conductor / type of feeder (C) which clearly substantiates how power loss can be reduced or minimized effectively.

Analysis of results

The study of feeder showcases the reduction in real power loss by:

• The transformer loading helps in reducing the power loss from 8.58% to 3.84% if we reduce the loading on the transformer.
• The technique of VAr compensation with Q optimization helps in reducing the power loss from → [(8.58: 6.54: 3.84) to (6.988: 5.181: 3.128) with 100%, 80% and 50% loading respectively].
• The technique of changing the conductor size / type of feeder from Rabbit to Coyote reduce the power loss from → [(8.58: 6.54: 3.84) to (3.42: 2.66: 1.59) with 100%, 80% and 50% loading respectively].

Thus the methodology and techniques used clearly shows the efficacy of in power loss reduction. These techniques are very scientific and accurate in handling the power loss as they help in reducing the quantum of power loss to great extent, thus, minimizing the loss of power. And they are also very financially viable and thus can boost the recovery of the game. The remedial measures suggested in the dissertation can help in ameliorating the poor power supply in our state and can address the power leakage in big way. As they say “A penny saved is penny earned”, similarly “A unit saved is unit earned”.

Fig. 3 shows the gradation from voltage drop to perfect voltage status by using the transformer loading, MVAr compensation and changing feeder/conductor.

Thus by the application of three distinct strategies-

• By restructuring of transformer or relocation of transformer,
• By VAr compensation incorporation at different busses and
• By changing the conductor size / type of feeder, we can certainly reduce the power loss at 11kV Feeder from 8.58 to 1.59.

When looked at a large scale the strategies can be very effective in addressing the power shortage in Punjab. As well as they are very economically viable. The restructuring strategies adopted of MiPower software can proved to be panacea for bridge the demand and supply of power in Punjab or India. On the whole, therefore, it is suggested that this innovative research should be applied immediately and urgently to meet the growing demand of electricity. As in terms of energy “A unit saved is equal to a unit earned”. If the suggested measures are adopted then definitely the tall promises are made in the manifesto that “Power for all in 2017” can definitely be meted out.

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