Download presentation
Presentation is loading. Please wait.
1
On Load Tap Changing Transformer Paralleling Simulation and Control
2
OLTC Overview Transformer Paralleling The need for control Current Solutions Our Plan and System 2
3
Parallel Transformers Increase Reliability Improve Power quality Prevent voltage sag Meet increased load requirements 3
4
Examples Illustrate the need for control Present Two Calculation Methods –Superposition Method –Admittance Method 4
5
Grainger Examples One-Line Diagram Grainger, Example 2.13, pg 78 5
6
Grainger Examples Per-Phase Reactance Diagram, Grainger pg 78 6
7
Superposition Method 7
8
8
9
Equivalent Circuit 9
10
Superposition Method 10
11
Admittance Method Grainger, Example 9.7 11
12
Admittance Method 12
13
Problem Definition We want to minimize the circulating current. Why? –Increased total losses of the two transformers –Unable to fully load one transformer without over-loading or under-loading the other –This current is parasitic, serving no benefit –The transformer is not operating at optimum 13
14
Project Objectives Build and test an experimental system –Measure the circulating current Build a mathematical model of the system Design a control scheme that utilizes SEL technology Refine the System to minimize circulating current over a variety of conditions 14
15
Popular Solution Methods. Master- Follower Method Power Factor Method Circulating Current Method Var Balancing (∆Var) Method TM Source: Advanced Transformer Paralleling Jauch, E. Tom: Manager of Application Engineering, Beckwith Electric Co., Inc. 15
16
Master-Follower Desired operation maintains same tap level on all transformers Consists of one control commanding transformer tap changes to follow 16
17
Master-Follower Positives: –Appropriate voltage level via load is maintained Negatives: –Does nothing to prevent circulating current 17
18
Power Factor (PF) Method Desired tap positions provide equal PF Done by comparing angle of currents Does not operate controls, Just prevents them from operating in the wrong direction. 18
19
Power Factor (PF) Method Positives: –Keeps PF in desired range. Negatives: –Difficult to apply to more than 2 parallel transformers. –If VAr flow, tap level changed is blocked to minimize PF difference. –If transformers have different impedances, Highest KW loaded transformer is forced to have highest VAr load. 19
20
Circulating Current Method Assumes continuous circulating current path Controls are biased to minimize Icirc. Higher tap lowered, as lower tap increased the same amount to make equivalent tap level. Relay used to block operation if tap level variation becomes to great. 20
21
Circulating Current Method Positives: –Icirc is put to a minimum –Initial voltage level maintained –Max difference in tap levels maintained Negatives: –Auxiliary CT’s are required –Flow of KW can not be fixed by changing taps »This causes oscillation of tap levels. 21
22
Var Balancing (∆Var) Method Loads transformers by balanced VAr sharing. Ignores KW loading 22
23
Var Balancing (∆Var) Method Positives: –Balanced VArs make Icirc a min or 0 –No auxiliary CT’s are needed Negatives: –Method is patented by Beckwith Electric Co. INC. 23
24
Our Plan SEL 3378 SVP assumes control of system Provided with phasors from the relay SVP calculates optimal tap levels SVP directs tap changers through SEL 487E relay 24
25
Our Plan Goals –Appropriate voltage level maintained –Icirc driven to a minimum –Max variation of tap levels met –Avoids tap level oscillation 25
26
System Transformers 487E Relay 3378 Synchrophasor Vector Processor 26
27
Transformers Two Autotransformers will be used to simulate two parallel power transformers Voltage controlled motors on the tap changers Transformer secondary will feed an external load from unity to 0.5 lead/lag 27
28
Transformers Superior Electric Type 60M21 Single Phase Input Voltage: 120V Output Voltage: 0V-140V KVA: 0.7 Toroidal Core Synchronous Motor –120VAC, 60Hz, 0.3A, 3.32 RPM 28
29
Transformers Short Circuit Tests –The resistance of the tap contact is larger than the reactance of the winding –The MVA imbalance of the parallel combination is expected to be dominantly Watts, rather than Vars Verified through no-load Paralleling test 29
30
T1 X and R Vs Secondary Nominal Voltage 30
31
Transformers The autotransformers do not exhibit characteristics similar to a typical power transformer Options –Use these transformers –Different Transformers, 5 kVA Motor driven autotransformers 31
32
Calculations The Superposition method will support the real component while the Admittance method will not –The real component will create a negative resistance in the PI equivalent 32
33
487E Relay Uses Lateral Logic 18 Current Channels 6 Voltage Channels Synchrophasor data collected once per cycle, up to 12 Channels 33
34
487E Relay Control transformer tap level Receives commands from SVP Displays: voltages, currents, Icirc, apparent power, real power, reactive power. 34
35
3378 SVP The SVP time aligns synchrophasor messages, processes them with a programmable logic engine, and sends controls to external devices to perform user defined actions. -SEL 3378 data sheet 35
36
3378 SVP Interface with the 487E Relay via serial connection. Phasor input to calculate circulating current. Control output to relay to minimize circulating current. Display output with real- time circulating current values. 36
37
37
38
Conclusion Proper transformer control results in reduced losses increased profits maximized quality and reliability 38
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.