Woodward 505HT, Инструкция по установке и эксплуатации

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Manual 35116 505HT for Pelton Turbines
Woodward 54
An integrating signal is a 4 to 20 mA signal that positions a proportional valve, or pilot stage valve. The
integrating signal is about 12 mA to center the proportional, or pilot stage, valve. When the current is less
than 12 mA the valve moves one way, and when the current is greater than 12 mA the valve moves the
other way. The further the signal is from the null current, the further the proportional valve plunger moves
from its center position. Typically, the proportional valve ports oil to another valve, or hydraulic amplifier,
which then positions the servomotor.
The integrating signal has two adjustments that must be made. The first adjustment is the “Valve Offset”.
The null current will probably never be equal to exactly 12.00 mA, so the valve offset makes up for this
difference. If this is not adjusted properly, the nozzle position will not match the nozzle position demand.
The second adjustment that needs to be made to the integrating signal is the “Valve Gain”. This controls
how much the current deviates from the null current for a given nozzle position error. If the nozzles are
sluggish to step changes, the gain can be adjusted to increase the nozzle response, or if the nozzles
overshoot during a step change, the gain can be adjusted to decrease the response. The control has an
“Offline Valve Gain”, which is used when the generator breaker is opened, and an “Online Valve Gain”,
which is used when the generator breaker is closed. If this feature is not to be used both these variables
must have the same value.
The Control has a dither function designed into its valve driver output. The valve dither function induces
an AC current on the actuator output. Valve dither accomplishes two things. First, it keeps the valve
plunger(s) constantly moving which reduces “stiction”, or static friction. “Stiction” can cause nozzle
hunting if the valve does not respond correctly to the electronic signal. Second, dither makes a positive
lap valve respond as though it were a zero lap valve. The control has 5 possible dither frequencies, which
are: 50Hz, 25Hz, 12.5Hz, 6.25Hz and 3.125Hz.
The Control continuously compares the actual nozzle position to the nozzle position demand in the
control. If they do not match within the “Minor Mismatch Window” for more than the “Minor Mismatch
Delay” time, the control will issue a “Minor Mismatch” alarm. If the nozzle position does not match the
demand within the “Major Mismatch Window” for more than the “Major Mismatch Delay” time, the control
will issue a “Major Mismatch” alarm. When a Major Mismatch occurs that referred nozzle is shutdown. If
all nozzles happen to have a “Major Mismatch” then a turbine shutdown is issued.
Manual Modes
The Control has two “manual” modes of operation, an “All Nozzle Manual” and an “Individual Nozzle
Manual”.
When “All Nozzle Manual” mode is enabled all automatic PID’s that were in control (Offline, Online or
Baseload) goes to tracking mode and the demand of all nozzles together can be driven manually. There’s
a tracking between Manual and Automatic modes. The nozzle position in this mode can be driven by
Raise and Lower commands (the same Raise and Lower speed commands used in automatic modes).
Direct setpoint can also be sent via Modbus or via display. The rate at which the manual position moves
is configurable.
Manual control mode can be enabled when the unit is running or when the unit is stopped. If “Individual
Nozzle Manual” is enabled for all used Nozzles then the “All Nozzle Manual” mode is also enabled.
The “All Nozzle Manual” demand shall be thought in terms of turbine
total flow, not in individual nozzle demand. Therefore depending on
the nozzle sequencing configuration the actual individual nozzle
demand will be greater than the Manual Nozzle Demand.
Released