QR: Generator Capability & V Curves

• Capability Curve is a plot of reactive power (Q) versus real power (P). Construction used for the derivation of a synchronous generator capability curve -

• The curve showing the relation between armature current and field current at a constant terminal voltage and with a constant real power is known as a V curve because of its characteristic shape.

QR: Generator OCC & SCC

• Open-circuit characteristic (OCC), also referred to as the open-circuit saturation curve, of a synchronous machine is a curve of the open-circuit armature terminal voltage (either in volts or in per unit) as a function of the field excitation (current) when the machine is running at synchronous speed.
• Short-circuit characteristic (SCC) of a synchronous machine is a curve of the three-phase short-circuit armature current as a function of the field excitation (current) when the machine is running at synchronous speed.
• The short-circuit ratio (SCR) is defined as the ratio of the field current required for rated voltage on open circuit to the field current required for rated armature current on short circuit.

QR: PID

PID Control Action:

U(s)/E(s) = K_p [1 + 1/(T_i s) + T_d s]

where
K_p is the proportinal gain or Gain,
T_i is the integral time or Reset time, and
T_d is the derivative time or Rate.

QR: First-order System

Transfer function:
C(s)     1
---- = -----
R(s)    Ts+1
Unit-step response:
Initially output c(t) is zero and finally it becomes unity. At t=T the value of c(t) is 0.632

QR: Closed loop System

Transfer function: C(s)/R(s) = G(s)/{1+G(s)H(s)}

QR: Hz vs RPM

The electrical frequency f of the voltage generated in a synchronous machine is


f = (Poles/2)*(N/60) Hz

where N is the mechanical speed in revolutions per minute (RPM), and hence N/60 is the
speed in revolutions per second (RPS).

QR: LVDT

Standard LVDT (generally from SCHAEVITZ Sensors) connections -
Primary (Excitation): RED & BLACK
Secondary (Position feedback): ORANGE & BLUE
With this connection output increases as actuator opens.

QR: Servovalve wiring

Servovalves from MOOG with Model No. G771K202 or similar have 3 coils and if their connection is made as below, cylinder extends -
Coil#1: RED (+) & WHITE (-)
Coil#2: YELLOW (+) & GREEN (-)
Coil#3: ORANGE (+) & BLUE (-)

QR: Ethernet cable

If it is a Straight connection then place the RJ-45 jack with pressable side down and open end towards you and follow this from left to right on both end of the cable -

1. White-Orange
2. Orange
3. White-Green
4. Blue
5. White-Blue
6. Green
7. White-Brown
8. Brown

For a Crossover connection, follow the above at one end and this on the other -

1. White-Green 
2. Green
3. White-Orange
4. Blue
5. White-Blue
6. Orange
7. White-Brown
8. Brown

Ping!

QR: 12 Series switches

Pressure, Differential Pressure, Temperature, or whatever it may be, if it is a 12 Series Explosion-proof DPDT Switch from United Electric Controls then -

Common - SW1: Brown, SW2: Yellow

Normally Closed - SW1: Red, SW2: Black

Normally Open - SW1: Blue, SW2: Violet

Ground - Green

Quick Reference (QR): 96FG-2A,2B,2C

96FG-2A,2B,2C are the TMR pressure transducers for measuring fuel gas interstage (P2) pressure in Gas machines. If they are Dynisco PT303 (4-Wire 0-5 VDC) then connections are -

White: + Excitation (to be connected to +24V at TBAI in Mark VI)

Green: - Excitation (to be connected to PCOM at TBAI in Mark VI)

Red: + Signal (to be connected to VDC at TBAI in Mark VI)

Black: - Signal (to be connected to RET at TBAI in Mark VI)

Replicating a Mark VI Device

This technique was used for Siddhirganj Unit-2. Unit-1 was commissioned. So we did not take any more pain to check the Unit-2 controller file (m6b). We simply replicate the Unit-1 m6b to Unit-2 m6b by the Device --> Replicate menu option. Gave the new device G2. Another thing we had to do. It was updating the Customer information according to the panel nameplate details. It should be remembered that updating Customer information results in Major difference. So panel has to be reboot.

Email posting

Trying blog posting via email. Hope this will work.

--------------------------------------------------------------
Ovi Mail: Making email access easy
http://mail.ovi.com

Composite Trip

Composite Trip was inevitable. It came all of a sudden and stayed there. What we got was positive supply not being extended to Trip Solenoids even after forcing Cross Trip signal (L4_XTP) to 0. Finally it came to us as a revelation that the problem was because of one of the 7 Trip contacts which may be connected directly to TREG Board for Emergency tripping. These contacts are to be Normally Closed so that positive supply can get extended to the terminals. One such contact of Generator Class-A trip (l86tgt1) was connected to TREG but it was Normally Open and the day it was connected our problem of Composite Trip (L5Cmpst_trp1) started.

The possible remedy was either use a NC contact of that trip or shift it to ordinary Contact Input terminal (TBCI). Since NC contact was not available at Generator Relay Panel, it was shifted to TBCI. Thus we could get rid of Composite Trip.

A New Series

Thinking of starting a new series related to my day to day troubleshooting experience. This would help for future reference not only to me but also to other unfortunate Engineers like me. Will try to make the posts as clear and simple as possible.

This is Windows Live Writer

This is a test blog post from Windows Live Writer. It may be helpful for quick blogging if I go for it anyway.

After a long time

I almost forgot about my own blog. Thanks to Google reader it has returned.