The Western Regional Electricity Board (WREB) grid system experienced a series of cascaded trippings and the total grid collapse in the month of April and May, 1995. Major 400 kV interstate tie lines were tripped resulting in blackout of important cities in the region.

The objective of this study was to simulate the actual disturbance events occurred in the month of April and May, 1995 and to submit the study results to Central Power Research Institute (CPRI), Bangalore. In addition to the simulation of the disturbance events, a few steady state contingency analysis were also conducted and the results were submitted.

WREB system is modelled up to 110 kV level. The 400 kV single line diagram (SLD) is represented for approximately forty eight lines (including S/C, D/C and T/C lines) and fifty five lumped generating stations. Further, the WREB system is having all the types of generation mix namely Hydro, Thermal and Nuclear.

Load flow studies have been carried out for base case as well as for contingency cases. It was observed that the load flow results for base case were very closely matching with the field values under pre-disturbance condition. Stability studies were also conducted for a 3 phase fault and single line to ground fault, followed by tripping of important 400 kV lines. For both steady state contingency cases and for stability studies, following results were submitted :

·         Real and reactive power flows through important 400 and 220 kV lines.

·         Voltage at important buses in the system.

·         The Steady state impedance seen by the relay on SLD.

·         Maximum rotor angle separation between generators.

·         Plots of generator frequency, terminal voltage, swing curve.

·         Plot of Impedance loci superimposed on actual relay characteristics (MHO relay and RAZFE relay).

Jindal Vijayanagar Steel limited is a flagship company of Jindal group setting up a steel plant, producing about 2.5 MT per year. The plant is synchronised to the grid at Munirabad at 220 kV voltage level. The plant is having four inplant generators of which two are 162.5 MVA and the other two of 12.5 MVA. The consultancy services offered for the integrated steel plant involves studies regarding stable operation of the plant, subject to wide variety of disturbances. Load flow cases were conducted to know the on-load transformer tap settings, which are used to maintain the normal inplant voltage at different grid voltage conditions varied from 178 kV to 230 kV at Munirabad and at a grid frequency of 48 Hz and 50 Hz. The short circuit study conducted revealed the information regarding the limitations of plant operation. The stability studies are carried out to determine the performance of the plant, to check whether the plant is able to pick up steel mill load with grid and during isolated grid operation. Since the plant is having a synchronous motor of 15.9 MW, a motor starting phenomenon is also carried out with grid and isolated condition to check that starting of large motor will not affect the performance of the other loads in the plant. Starting of a motor with and without auto transformer, with load and no-load was also studied.

Jindal Strips Limited is a flagship company of Jindal organization setting up 500,000 tons/annum integrated steel plant at Raigarh (Madhya Pradesh). The plant is interconnected with Madhya Pradesh Electricity Board (MPEB) at 132 kV substation at Raigarh. To increase the production capacity of the plant, additional generator is added to the captive plant. The study is conducted to ensure the stable operation of the plant at all times. The main objectives in the study are -

·         Study is conducted to balance the total system generation against the load and losses and to maintain the desired power exchange with the grid.

·         Computation of fault levels at different buses within the system, to select the breaker ratings.

·         System synchronization with grid.

·         To suggest different system islanding schemes.

·         To study the transient behaviour of the system for different faults in the plant and to suggest protective measures.

·         To find the behaviour of the system during motor starting in the emergency scheme.

·         To study the effect of arc furnace load

The load flow study is conducted at different grid voltages, the system voltages were found to be satisfactory. Keeping in view the restriction on the fault level at 11 kV buses (inplant generation by six turbo generators with two D.G sets in parallel ), split operation of the plant was recommended. From the transient stability studies, it is found that the generators are to be equipped with AVRs and Governors. The turbine governor control system is in operation either as constant power mode or constant frequency mode depending on the status of the grid connection. The motor starting was found to be satisfactory in the emergency scheme of the plant. To improve the arc furnace performance and to reduce the flicker severity, Static Var Compensator is recommended.

DCL a consultancy organisation, entrusted the development of transient stability analysis package for a power system with exciter and governor controllers to PRDC. A Free programmable block study was carried out using transient stability analysis package of MiPower.

Static excitation system, Hydraulic governor with automatic power and frequency regulator, Electro hydraulic turbine controller and Gas turbine governor associated with the generators are modelled by using free programmable blocks (FPB). For Computer simulation, control block is simplified to a simple elementary blocks like adder, integrator, filter, gain etc. The stability studies were carried out for different disturbances like motor starting , three phase fault, single line to ground fault and Load shedding by representing the AVR and Governor as FPB. The system voltage, frequency, response of the static exciter, governor are observed for the above disturbances.

Tata Iron and Steel Co. Ltd. (TISCO), the pioneer in steel industry has taken up various modernisation works to increase production and improve the overall efficiency of the plant. However, during operation TISCO was facing frequent failure of electrical components in their Hot Strip Mill (HSM) plant. In this regard the study was conducted to find the cause of failure and to suggest suitable measures to overcome the abnormal conditions that leads to equipment’s failure.

Using the EMTP type of transient analysis repeated switching studies are conducted under various system conditions and following observations were made-

·         The cause for the problem was found to be a vacuum circuit breaker (VCB), which chops before natural current zero (@ 5 A). The maximum over voltage is observed during inrush current breaking of unloaded transformer, which is considerably more than the Basic Insulation Level (BIL) of the equipment's.

·         Surge arresters of appropriate rating with proper insulation level and energy dissipation capability are recommended at the primary of the transformer, to mitigate the over voltage occurring in the system.

Among many of the long term measures planned for augmentation of generation by Karnataka Electricity Board, Upper Krishna Power project (UKP) is the one, which is being setting up by Chamundi Power Corporation (CPC). It consists of 297 MW power house at the nearly completed Almatti dam, and a cascade of 4 power houses at the down stream of Narayanpur dam providing another 809 MW, amounting to a total generation of 1106 MW.

This project was envisaged to PRDC for a phased transmission expansion plan to evacuate power from Almatti and Narayanpur plants. The objectives of the study are -

·         To evolve a phased transmission evacuation plan based on the year-wise load projections and anticipated generation availability for the years 1999 to 2004.

·         To perform steady state power flow analysis for both Peak load and Light load conditions for each of the years ( 1999 to 2004 ).

·         To perform contingency studies for credible transmission line outages with a view to ensure system security.

·         To evaluate steady state fault levels by performing fault studies.

·         To evaluate system stability for major grid disturbances in order to determine fault clearing time and inertia of Almatti and Narayanpur machines.

·         To evaluate steady state over-voltages during line charging and line opening conditions and to suggest proper compensation requirements, if found necessary.

About the Client:

The National Aluminium Company Limited (NALCO), a Government of India Enterprise, the pioneer in Aluminium industry, is one of the country’s largest integrated Aluminium manufacturing unit, situated at Angul, in the state of Orissa. The plant is connected to the GRIDCO grid at 220 kV level. M/s. NALCO owns and operates an aluminium plant with an operation capacity of approximately 2.3 tpa with a future expansion plan to 3.45 tpa. The total power requirement of smelter plant including auxiliaries is about 410 MW. M/s NALCO have their Captive Power Plant (CPP) consisting of six units of 120 MW each exclusively to meet the energy requirement of the Aluminium Smelter plant. Generally, the CPP units are operated in synchronism with the GRIDCO Grid.

About the Studies conducted:

The objective of the studies were to find out voltage conditions, adequacy of transmission, stability of the CPP machines, functioning of protection system and co-ordination of overcurrent relays, frequency & voltage variation in the plant during normal and abnormal operating conditions. Also, to assess the NALCO-plant behaviour due to external grid disturbances. A brief details of the study is listed below.

·         To conduct the existing plant study representing the NALCO plant in detail and GRIDCO grid of 400 kV, 220 kV, 132 kV and all the generating units in the GRIDCO.

·         To conduct the future planning studies looking into future expansion of NALCO plant and also GRIDCO Grid.

·         To conduct analysis on the plant dynamic behaviour with outage of partial or full smelter load both in the interconnected mode and islanded mode of operations taking in to consideration the present and future expansions in the plant and in the grid.

·         To conduct stability studies, both transient and dynamic by initiating three phase faults and single line to ground faults at important buses in the plant as well as in the grid.

·         To analyse the effects of loss-of-load and loss-of-generation in the grid as well as in the plant.

·         To assess the contribution of sequence currents by CPP due to major open conductor faults (One phase and two phase open).

·         To analyse the existing islanding scheme and to suggest the improved islanding scheme.

·         To conduct the large HT motor starting analysis in the plant.

·         Analysis of present protective system and measures to be undertaken for strengthening of the same under various operating conditions. Further to conduct overcurrent relay co-ordination studies for the plant.

About the client :

M/s Central Power Research Institute (CPRI), one of the country’s pioneer research institute in Electrical Engineering, caters to needs of power utilities, industries and consultants. CPRI is established in the year 1960 and situated at Bangalore, in the state of Karnataka. CPRI mainly consists of various laboratories namely, High Voltage Lab., High Power Lab., Power System Simulation Lab., Short Circuit Lab. etc. CPRI has a power supply arrangement with Karnataka Electricity Board (KEB) and receives power from grid at 220 kV level. CPRI’s electrical distribution system mainly consists of 220 kV, 33 kV, 11 kV and 0.415 kV voltage levels. The contract demand of the CPRI is 3500 kVA.

About the studies conducted:

The main objective of the study is to determine the fault currents at the 220 kV, 33 kV, 11 kV and 0.415 kV voltage level, achieve proper over current relay co-ordination and to determine relay settings of the relays in the CPRI distribution system. Most of the system data used in the study have been made available by CPRI-HPL engineers. The brief details of the studies conducted are listed below.

·         To develop the Single line Diagram (SLD) and database for CPRI distribution network..

·         To develop the relay database of Relays in CPRI system.

·         To carry out the short circuit study.

·         To carry out the relay co-ordination study and to determine settings of the over current relays.

·         To determine settings of transformer differential relays in the CPRI system.

M/s. Karnataka Electricity Board in association with Indian Institute of Science, Bangalore had conducted the power evacuation studies for evacuating power from Mangalore region. The 400 kV lines identified for evacuation of power from Mangalore region towards Bangalore and Mysore are as follows -

Two 400 kV Double Circuit lines from Cogentrix to Hassan 180 km.

One 400 kV Double Circuit line from Hassan to Mysore 100 km.

One 400 kV Single Circuit line from Hassan to Nelamangala 140 km.

One 400 kV Single Circuit line from Mysore to Nelamangala 165 km.

During the study, the light load to peak load ratio was taken as 67%. Based on this figure, the shunt reactor compensations were computed for controlling the voltages during low load condition. However, from the actual load observation recorded at the load dispatch centre, the light load is as low as 40% of the peak load during few hours in a year. For 18% of the time period in a year, the light load is below 50% of the peak load. Hence it was decided by JVCC - KEB that shunt reactor compensation requirements have to be reworked out for the light load to peak load ratios of 0.5 and 0.6.

Power flow studies was conducted for the base case with light load to peak load ratios of 0.5 and 0.6 . During this, buses which are exceeding maximum limit mark ( voltage above 1.05 pu) are identified and suitable reactive compensation at 400 Kv level was suggested. Further KEB/JVCC were interested in conducting studies with the removal of some major lines and generations . Studies were also conducted for the contingency cases suggested and suitable reactive compensations were suggested.

During the above studies / contingency cases the following points are taken in to account

·         Only very lightly loaded minimum 400 kV lines and 220 kV lines have been switched out and it is ensured that alternate paths are available for power transfer for each alternative study.

·         The voltages for all 400 kV, 200 kV, 110 kV and 66 kV buses are controlled to be within 1.05 pu.

·         It was recommended to switch off all the shunt capacitors in the system during light load condition . During peak load condition it is recommended to switch off the bus reactors wherever necessary.

·         Flexibility in operation when the load goes slightly below 50 % of the peak load (based on additional reactor compensations recommended)

·         TNEB and APSEB systems are also represented for light load conditions and voltages at CUDPH, SALEM, GOOTY, and NGSGR are controlled to be around 400 kV.

M/s. Visvesvaraya Iron and Steel Ltd. (VISL), a subsidiary of Steel Authority of India Limited (SAIL), have their steel plant located in Bhadravathi town, Karnataka. VISL has a power supply agreement with Karnataka Electricity Board (KEB) to meet the power requirements of the entire plant. The main source of electric power supply to the plant is by three numbers of 110 kV feeders which are emanating from the KEB's 110 kV Main Receiving Station (MRS) located in Shimoga.

In view of the inconsistent power supply situation in the state and to meet critical loads of blast furnace, VISL had installed a captive power plant in the year February / March 1995. The 7.5 MVA D.G. set alone is not enough to start 3 MW blower motors. Also considering starting of H.T. Motors, the D.G. set alone cannot meet the load demand. Further, in case of grid supply failure, the DG has to take over instantly the essential loads. It is thus customary to run the DG set continuously in parallel with the KEB grid.

VISL would like to have the flexibility in power supply distribution so as to use the DG power optimally, which requires the synchronisation of DG supply with the KEB gird. In view of paralleling of DG supply with KEB grid, existing control, protection, optimum relay settings and interlocking arrangements need to be reviewed under all the operating conditions.

The power system study for the plant to arrive at the optimum relay settings of the relays used in DG islanding scheme was entrusted to Power Research and Development Consultants by the Deprocon Engineering Private Ltd., Bangalore.

The main objective is to study and suggest the different relay settings of relays incorporated in system islanding scheme namely, under frequency relay, df/dt relay and reverse power relay. For the system to be reliable, it would be capable of withstanding wide variety of disturbances. Starting of H.T. motors are also analysed. The stability studies for different types of disturbances were also conducted to arrive at the optimum settings for the above relays.

M/s JK Corporation Limited (JKCL) is one of the large-scale paper manufacturers in India. M/s JKCL has its paper mill at Jayakaypur in Rayagada district of Orissa State. The mill is connected to GRIDCO grid at Theruvali 220/132 kV substation by 9.7 km single circuit 132 kV overhead line of Panther conductor. M/s JKCL also has its own captive generation with installed capacity of 19.9 MW consisting of 12 MW, 5.4 MW and 2.5 MW Turbo Generators. Grid power at 132 kV is stepped down to 6.6 kV using 15 MVA 132/6.6 kV transformer. Figure 1 shows the single line diagram of the electrical system.

In view of the inconsistent power supply situation in the state and to meet critical loads of blast furnace, VISL had installed a captive power plant in the year February / March 1995. The 7.5 MVA D.G. set alone is not enough to start 3 MW blower motors. Also considering starting of H.T. Motors, the D.G. set alone cannot meet the load demand. Further, in case of grid supply failure, the DG has to take over instantly the essential loads. It is thus customary to run the DG set continuously in parallel with the KEB grid.

M/s JKCL is able to supply the power to different plants by isolated operation of all the generators and also the grid. 12 MW TG supplies an average load of 9.4 MW. Generator G1 is 5.4 MW rated and generally load on this generator is in the range of 4.2 MW to 5.3 MW. It supplies an average load of 4.6 MW consisting of water supply, CF-5, CF-4, CLO2 and TDR plants. The generator G2 is rated at 2.5 MW. Load on this generator is 1.8 to 2.3 MW with an average load of 1.9 MW consisting of Boiler-1, DDR, and chipper and KIOSK plants. The load on grid import varies from 4 to 4.2 MW with an average load of 4.1 MW consisting of fiber line and chipper plants. Figure 2 shows the existing isolated operation of the grid and generators with their connected load. However, it is found that due to isolated mode of operation, huge losses to the tune of RS 1 crore are incurred when the 12 MW TG is out or not able to supply the full load. In this context, it is decided to conduct the feasibility study to determine the synchronization scheme so that the 12 MW TG can be run in parallel with the grid.

In the proposed system, M/s JKCL intends to synchronise the 12 MW unit with the GRIDCO grid and run the unit in parallel with the grid. In this context, the responsibility of conducting the feasibility study and arriving at the suitable synchronization scheme was entrusted to M/s Power Research & Development Consultants Pvt. Ltd. (PRDC), Bangalore by M/s ABB the prime vendor for supply and commissioning activities. The following were the main objectives of the study

·         To determine the fault level when the 12 MW unit is synchronized with the grid and to design suitable reactors to limit the fault level.

·         To conduct stability studies to determine the system islanding and load shedding schemes.

·         To suggest suitable protection and metering system for the synchronization.

·         To suggest modification/change in the governor control for constant power/frequency mode of operation.

·         To bring about the limitations of synchronization with the grid.

Jindal Strips Limited a $ 260 Million plus ISO: 9002 & ISO: 14001 is the flagship company of the Jindal Organization. The company has come a long way from a single factory establishment, started in 1970. It is the largest integrated manufacturer of quality Stainless Steel in India & single-handedly caters to 40% of the total demand for stainless steel in India. From Stainless Steel Hot Rolled/Cold Rolled Coils, Plates and Flats, Slabs and Blooms are produced keeping both national as well as international standards in mind.

At Hisar lies India's only fully integrated Stainless Steel plant. Located in the state of Haryana M/s Jindal Strips Limited have a production capacity of 250,000 to 300,000 tones per annum. From point of power system configuration, at present, JSL Hisar plant is having 3 nos. of 12.5/16 MVA transformers of 132/11 kV connected to HSEB Grid with a contract demand of 26 MVA. The remaining part of the plant demand is met by in - house generation of about 40 MW accomplished by 6 Diesel Generators at 11kV all operating in parallel with the grid. Mainly JSL - HISAR is having 2 no. of arc furnaces one rated 18 MVA and the other 24 MVA. M/s JSL was planning to replace 18 MVA Arc Furnace with 36 MVA and add a new generation of about 6 MW to the system. In this regard, Electrical system studies for carried out to determine the capability of the existing system configuration and proposed configuration. The main objective of the study is summarised as below

·         Load Flow study to determine the system adequacy on present 132 kV and 11 kV system after 18 MVA Arc furnace replaced with 36 MVA Arc furnace.

·         Short circuit study to find out short circuit levels at different buses at JSL premises for the existing configuration as well as new configuration

·         Stability studies for the proposed plant to compute

·         Voltage dip

·         Extent of voltage dip when both furnace act simultaneously

·         Harmonic power flow studies based on the typical harmonic content of the EAF to determine the harmonic voltage and current distortion at the point of common coupling and other buses.

Jindal Steel and Power Limited (JSPL) is one of the group companies of Jindal organisation having 5 lakh/annum integrated steel plant at Raigarh (M.P). The plant is interconnected with the MadhyaPradesh Electricity Board (MPEB) grid, at 132 kV substation at Raigarh. As an expansion plan, M/s JSPL intends to setup 77 MW power plant, 50 MVA rolling mill plant, 50 MVA smelter plant and to enhance the existing 30 MVA arc furnace capacity to 50 MVA.

The main objective of the study was to determine the feasibility of the system for the above said system expansion. A brief detail of the study is listed below

·         To study the adequacy of the 132 kV feeder in catering 50 MVA EAF load, 77 MW Power plant, 50 MVA rolling mill load and 50 MW smelter plant.

·         To study the 220 kV interconnection option if the 132 kV interconnection option is not feasible.

·         To compute the short circuit levels at different buses at JSPL premises.

·         To conduct the load flow and stability studies for the proposed plant to compute

·         Voltage dip

·         Extent of voltage dip when EAF is short circuited

·         To conduct the harmonic power flow studies based on the typical harmonic content of the EAF to determine the harmonic voltage and current distortion at the point of common coupling & other buses

·         Tuned harmonic filter bands

·         Static var compensation (SVC).

·         To conduct detailed analysis to minimise the harmonic distortion and voltage depression by suitable measures like:

·         Tuned harmonic filter bands

·         Static var compensation (SVC).

·         To design the system keeping in view the total flexibility of power import as well as export.

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