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CHAPTER 1: INTRODUCTION
1.1 DESCRIPTION
Tripping means the interruption in electricity supply. An electric line is tripped if it starts carrying the fault current or it get broken or due several other reasons. It is a protective measure which essentially isolates the faulty lines from the rest of the healthy sections. So basically cascade tripping is a tripping of protective devices to isolate the part or parts of the system to avoid the damage to the load and the system equipments. Sometimes tripping of power grid takes place due to unbalanced condition is also called as cascade tripping.
Modern power systems experience many disturbances and majority of that are eliminated by relay protection and emergency control system. According to historical data , relay miss-operation is one of the contributing factor of 70% of major disturbances in the power system. With rapid growth of loads , transmission distances , HVDC and FACTs devices , the dynamic behaviors of power system are getting more and more complicated. A single fault is unlikely to destroy a modern power system , but information deficiency , hidden failures of relays , faults of other secondary system or human errors may be the cause of cascading events and the system, however strong may evolve in to power calamity.
Cascading outages may happen in AC lines, DC lines, AC-DC line, sending area and receiving area as well.
1.2 INTRODUCTION OF PROBLEM DEFINATION
When the load demand is larger than the power generated the frequency of the machine goes down. When the value of his frequency lowers than the nominal value of the frequency the grid trips and the loss of power occurs. These power failures are not normal, they sometimes lead to blackout conditions if there is no backup protection available.
In power grid when one of the component fails and then its load is shifted to nearby system. Those nearby systems may push to work beyond their capacity so they get overload and shift their load to another system. Cascade failure mainly seen in high voltage systems where a single paint failure on a completely loaded or somewhat overloaded system results into surges of spikes across the system.
Once power is generated it has to be supplied to somewhere else. If it is than the load demand it will cause voltage surge or if it is less it will cause voltage dips. For proper operation of system, synchronization must be kept with the load. Power grid can withstand a single event that is single generator failure or single transmission line failure. This is called as N-e contingency planning. The system can collapse if several failures takes place in rapid succession.
CHAPTER 3: BRIEF THEORY RELATED TO PROJECT WORK
3.1 BASIC WIRING AND SCHEMATIC DIAGRAM OF PLC AND SCADA BASED CONTROL SYSTEM
If generator 1 load demand will increase then we have to share the load. So for that we are doing load sharing in which some amount of load will be shared on another generator 2.
If load demand is increasing out of capacity in that condition we have to use load shading in which all over load will be disconnect from generator and generator will be safe.
During shading condition PLC gives a signal in that condition all load work on the external source for some time. After that when healthy condition occurs then all load transfer to the system alternator and backup system automatically out from system.
We occurring fault manually. In that condition if fault occurs in particular line then it indicates on SCADA and which fault occurs is also shown.
3.2 LOAD SHARING
PLC compares the reference value of main alternator and connect to second alternator through relay according to reference voltage Designing an efficient and cost effective solution for replacing or changing the alternator that is Problem related to alternator when it was fail then it can be handle and control by PLC.
3.3 LOAD SHADING
With a Programmable Logic Controller (PLC) scheme, load shedding is initiated based on the total load versus the number of generators online and/or detection of under-frequency conditions. Each substation PLC is programmed to initiate a trip signal to the appropriate feeder breakers to shed a preset sequence of loads.
In this work, a fault detection and diagnostic module is described based on internal PLC program signal data which is acquired through OPC Server. The observed or real-time PLC signal data is compared with normal PLC signal data to find out possible faults or deviations. The data acquisition procedure and the techniques used have been explained in this paper.
BACK UP SYSTEM
According to the International Electro technical Vocabulary, backup protection scheme is intended to operate when a power system fault is not cleared or an abnormal condition is not detected in the required time because of failure or inability of other protection to operate or failure of the appropriate circuit breaker to trip. The backup system is, by definition, slower than the main protection. Backup system may be obtained automatically as an inherent feature of the main system scheme, or separately by means of additional equipment.
CHAPTER 4: SIMULATION & RESULT ANALYSIS
There are 3 lamp as shown in the simulation which is considering as load of each ALTERNATOR, which are interconnected.
As shown in simulation Generator 1, 2 and 3 are supplying the power to the lamp 1,lamp 2 and lamp 3 through grid.
Load demand is balanced by using PLC through which load sharing, load shading and backup condition is possible.
If generator 1 load demand will increase then we have to share the load. So for that we are doing load sharing in which some amount of load will be shared on another generator 2.
If load demand is increasing out of capacity in that condition we have to use load shading in which all over load will be disconnect from generator and generator will be safe.
During shading condition PLC gives a signal in that condition all load work on the external source for some time. After that when healthy condition occurs then all load transfer to the system alternator and backup system automatically out from system.
We occurring fault manually. In that condition if fault occurs in particular line then it indicates on SCADA and which fault occurs is also shown.
CHAPTER 5: COMPONENT DETAILS
PLC(PROGRAMMABLE LOGIC CONTOLLER)
They can be design for multiple arrangements of digital and analog I/O extended temperature ranges, resistance and vibrations and impact etc.
This function is discrete inputs are given a unique address and PLC instruction can test if the inputs state is on or off.
A Programmable Controller is a specialized computer. Since it is a computer, it has all the basic component parts that any other computer has; a Central Processing Unit, Memory, Input Interfacing and Output Interfacing. A typical programmable controller block diagram is shown above.
5.1.2 Selecting a PLC:
After the planning phase of the design, the equipment can be ordered. This decision is usually based upon the required inputs, outputs and functions of the controller. The first decision is the type of controller, mini, micro, or software based. This decision will depend upon the basic criteria listed below.
Number of logical inputs and outputs.
Memory – Often 1K and up. Need is dictated by size of ladder logic program. A ladder element will take only a few bytes, and will be specified in manufacturers documentation.
Number of special I/O modules – When doing some exotic applications, a large number of special add-on cards may be required.
Scan Time – Big programs or faster processes will require shorter can times. And, the shorter the scan time, the higher the cost. Typical values for this are 1 microsecond per simple ladder instruction
Communications – Serial and networked connections allow the PLC to be programmed and talk to other PLCs. The needs are determined by the application.
Software – Availability of programming software and other tools determines the programming and debugging ease.
The process of selecting a PLC can be broken into the steps listed below.
1. Understand the process to be controlled (Note: This is done using the design sheets in the previous chapter).
List the number and types of inputs and outputs.
Determine how the process is to be controlled.
Determine special needs such as distance between parts of the process.
2. If not already specified, a single vendor should be selected. Factors that might be considered are, (Note: Vendor research may be needed here.)
Manuals and documentation
Support while developing programs
The range of products available
Support while troubleshooting
Shipping times for emergency replacements
Training
The track record for the company
Business practices (billing, upgrades/obsolete products, etc.)
3. Plan the ladder logic for the controls. (Note: Use the standard design sheets.)
4. Count the program instructions and enter the values into the sheets
Then that output of converter give to the analog to digital converter of PLC. It convert ampere value in terms of digital data because PLC read digital data. We give up to 200ma to the PLC which is converted by converter.
In our panel we are using 5:1 C.T. and it gives the output to the converter.
This Converter input is 0-5 Amp and output is 0-20ma. And 24DC/230AC input and 0-10 AC/DC output.
It gives data to PLC Analog to Digital Converter and as predetermined data plc operate the function of load sharing, load shading.
Relay Card
Relay are switches that open and close circuits electromechanically.Relay control one electrical circuit by opening and closing contacts in another circuit.
When a relay contact is Normally open(NO), there is an open contact when the relay is not energized. When a relay contact is Normally closed(NC), there is a closed contact when the relay is not energized.
In either case, applying electrical current to the contacts will change their state.Relays are generally used to switch smaller currents in a control circuit and do not usually control power consuming devices except for small motors, LED lamp.
FIG-14-RELAY CARD
Nonetheless, relays can control larger voltages and amperes by having an amplifying effect because a small voltage applied to a relay coil can result in large voltage being switched by the contacts.
Protective relays can prevent equipment damage by detecting electrical abnormalities, including overcurrent, overload and reverse currents.
CHAPTER 6: COMPONENT COST
SR.NO. COMPONENT NAME SPECIFICATION QUANTITY COST
1. Current Transformer 5:1amp 1 550
2. C.T. Converter 0-10V,0-20ma 1 2500
3. MITSUBISHI PLC 14 I/P, 10 O/P 1 12000
4. Analog to Digital Converter 8 chanel 1 4500
5. Pushu button 24 volt dc 11 275
6. 1 way switch 230 volt ac 3 90
7. Relay Card SPDT, 1 1000
8. Indicator 230volt A.C. 6 180
9. Lamp 230v,100w 5 100
10. Lamp holder —– 5 75
11. Plywood 4:3 m 1 150
12. Stand —– 4 60
Total:- 21475
CHAPTER 7: APPLICATION
There are many applications for PLCs in substation automation, distribution automation and SCADA systems. As utility engineers become more familiar with the capability of PLCs and PLC manufactures develop new substation specific products, the number and type of potential
Applications continue to increase.
Analog and Discrete I/O
Metering and station information management
Protection and control
Circuit breaker lockout
Protective relay interface/interaction
Dynamic protective relay setting for dynamic station topology
Automatic switching
Emergency Load Shedding
Re-routing services for station maintenance
Automatic transfer schemes
Load sectionalizing
Custom, automatic reclosing schemes
Circuit breaker control and interlocking
Feeder automation and fault recovery
Voltage regulation management
LTC (Load Tap Changer) Control
Voltage regulator control
Transformer management
Parameter monitoring and alarming
PLC and communications self monitoring
Maintenance and Safety
Demand Control
Synch check and generator synchronization.
CHAPTER 8: CONCLUSION AND FUTURE SCOPE
With application of this protection system in existing power system results in less prone to blackout or brownout condition.
Load sharing, Load shading easily applicable in the system. Fault is also analyzed by this panel. If shading occurs then Power backup is apply instantly.
So for the power continuity of the supply without any load shading condition this system will applicable.
By using PLC and SCADA all over system will fully automatic control, Load sharing will be accurate share in all alternators; load shading will occur at the instant therefore no damage to the alternator.
This system is also applicable at industrial sector as well as commercial sector. At which high amount of load supply and large amount of working process at every time.
By using PLC and SCADA in the system fault will easily detect and solve at the instant. And in faulty condition power continuity is ease from another side and getting time to remove fault.
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