Digital Electric Hydraulic

General Description

Structure

MMI & Functions

Turbine Startup Procedure

Hot topics

DEH is one of the most fast, important and mysterious system in the power plant. It controls the turbine to Startup, warm up, synchronize with grid, loading, load rejection and so on, monitor the turbine condition continuously. DEH is a close-loop system. with operator’s demand, it adjusts the turbine to the most optimum condition automatically. It communications with the third-party system freely. We can achieve Boiler-following, Turbine-following and so on easily.

Let’s enjoy this wonderful system right now.

DEH Assembly

1 Engineer station (DROP201)

1 Operation station(DROP215)

2 cabinets with 2 pairs DPU

2 switches (root & fan out switches)

IO cards (TC, SS, VP, AI, AO, RO and so on)

Printer (Picture & Logic Print)

SYSTERM STATUS

Drop 41&91, Drop 42&92 are redundant, each of pair’s failure will never cause system malfunction. Drop41&91 are for Turbine Control (Operator automation) and OPC (overspeed protection). OA is in task 3 of 100 ms cycle time, OPC is in 4 task with 50 ms or less.Drop42&92 are for Turbine’s thermal stress calculation and ATC (automatic turbine control). logics and measuring points should be in task 2 of 1000 ms cycle time.Switches are redundant and support for TCP/IP network. We can communication with any Third-Party equipments.Printer, IO cards and so on are the same with DCS.

Note: we are supposed to well know of Ovation.

Overview control picture

Main Human-Machine-Interface.Demands entrance: turbine latch, control mode, valve mode, speed & load target, rate and so on.Parameters indication: main& reheat steam pressure, temperature, valve’s lifting, general alarm message.

Note: let’s check main function of each pictures, sub pictures.

Control mode

Pick up each mode .

Operator auto is recommended, and it’s most popular in power plants.

Manual is not recommended even operator is thoroughly familiar with turbine and control system.

All the other modes are deactive, turbine picks up manual mode.

Manual panelIt’s recommended to pick up manual mode under unavoidable contingencies only. It is an open loop type of control in which the operator position the valves by pushing buttons.In this mode, operator should monitor operation parameter strictly.

Feedback loops

First Stage Pressure is linear with the turbine load and a proximate indiscrimination control.MW Loop is an accurate indis-control. Actual load follows the target load strictly.Fre-control help the grid to keep frequency steady.

Note: all the loops should be activated after breaker closure and be activated in the same time but not recommended.

valve limiter provides with high-limiting action on the final GV controller output. The valve position limiter setpoint can be set on the set limiter graphic manually or automatically by turbine latching.High & Low load limiter limit the load set point after main breaker is closed.On manual mode Load Limiters will not work. Limiters’ setpoints should never be out of the range.

Limiters

TV-GV Transfer should be activated manually at steady 2900RPM, and it’s an one-directional transfer.After TV-GV Transfer, GV is in single mode automatically, and move synchronously.After about 6 months’ turbine operation, transfer turbine to Sequential mode to increase turbine’s efficiency. The advantage will be distinct especially in the low load range.Recommended vlv sequence: 1,2/4/3. We can tune the sequence according to turbine vibration, bearing temperature supervised by manufacture.

Valve mode

Tests should take after breaker’s closure.

To hold the load in the test, remaining vlvs will open automatically to compensate the load reducing.

In TV test:

1.Close GVs of this side to totally close position.

2. Close TV and open.

RSV & IV tests are the same with TV’s & GV’s

Vlv test

Note: never test two or more vlvs on both side

Push OPC TEST button to test the OPC solenoid and check the GV fast close time(<500ms). It can be used for GV seal test.

before taking electric or mechanical over speed test, we should forbid OPC. Because OPC initiating speed is 3090rpm while electric over speed is 3300rpm,mechanical overspeed is between 3300rpm and 3400rpm.

OPC has LDA function (Load Drop Anticipator).

OPC MODE

Note: OPC solenoids are DC,It’s recommended not to energize them too long time.

Turbine Startup

In guangninh project, we would like to choose the HP startup with bypass interface off.

All peripheries are supposed to ready.

First startup should accord with the startup curve and operation instruction strictly.

Note: this procedure include most startup functions but all.

Startup curve

Startup procedure

Check Engineer station and all equipments. Make sure all the valves can move freely.

Pick up Operator Auto Mode, Bypass interface off mode, latch the turbine (hold the button for about 2s).

Check Valve limiter increases to 100% automatically, all GV,RSV and IV are totally open, TVs are closed.

Test OPC function, make sure GVs can close immediately with OPC solenoid energizing.

Make sure: turning gear is running, Vacuum breaker is closed and vacuum should be as less as possible, Drain valves are open.

Everything is ok. Enter a 600rpm target speed and 100rpm/m rate, and go.

TV will open slowly and the speed will increase to 600rpm. Turing gear will disengage automatically at about 200rpm.

Hold in 600rpm long enough to check TSI. Make sure turbine acceleration is less than 0.076mm.

Trip the turbine. (hold at least 4min in 600rpm)

Note: turbine is ready to roll with steam now

Note: set point in bearing resonance range is invalid.

Holding in other resonance ranges is invalid.

Startup the turbine again according to last procedure again.Accelerate turbine to 2900rpm With less than 200rpm/m rate and hold.If the cylinder, steam chest, shaft temperature is not satisfied. Turbine should be held for warming up at nearest speed about 2080rpm-2350, but never in the resonance range.TV-GV transfer. Make sure when GVs are closed, speed should drop more than 30rpm.

After TVs are totally open, accelerate turbine to 3000rpm with 100rpm/m rate.

Hold at 3000rpm to check stability of speed. Wait generator breaker closing.

As usual, we check the ETS trip now.

If turbine is trip manually, startup it again with a rate a little bit larger (recommend 200rpm/m to 250rpm/m).

Note: before TV-GV transfer, make sure steam chest’s indoor-face temperature is more than saturation temp. It’s calculated as following.

Ts=T1+1.36 （ T2-T1）Ts: steam chest indoor-face temp.

T1: steam chest outside wall temp. measured by thermal couple.

T2: steam chest inside wall temp. measured by thermal couple.

Note: speed rate in resonance range will switch to 500rpm/m automatically.

When the generator breaker is closed, DEH set about 5% initial load immediately. Make sure turbine will never be a dangerous motor.Load the turbine and take tests.

Note: Hold at 5% load for at least 30 minutes plus one additional minute for each 2℃ of throttle steam inlet temperature change during the hold period.

Hold turbine at 10% of rated capacity. for at least four hours immediately before over speeding the turbine.

Generator breaker closed, 1 min later, the HEV (HP VENT VALVE) will close, cold reheat pressure increases slowly, HP EXHAUST NO-RETURN VLV is opened slowly by the HP exhaust pressure automatically.

Turbine load increased to 10% of rated capacity, HP drain VLVs should be closed. At 15% of rated capacity, LP Spray Solenoids should be closed, at 20% of rated capacity, IP drain VLVs should be closed.

Notes

Hot topic for frequency loop

More than about 20% of rate capacity, we can active frequency loop.

When the frequency of grid descends, turbine increase load automatically. contrarily, the same.

The quantity of the turbine increasing load is different according to different capacity of grids. We get this curve from local grid.

In order to protect the turbine, freq. loop can never reduce the load to a minimum value. (about 20% GV steam flow)To keep operation stable, set a dead band for freq. loop. On the same grid, according to same grid frequency fluctuated, the turbine’s load variety will be different a little bit to keep stability of the turbine operation.We should tune the parameters according the request of the grid.

F1(x) for dead band and Range of the fre. Loop.

F2(x) for quantity of load Increasing curve.

F3(x) for making sure stabilityOf turbine, responsible curve

According to the last logic:

1. We suppose the turbine is running on rated parameters and load . Grid frequency increased 6 rpm.

The quantity of load decreasing is 12MW.

The diversity factor is 5%.

Note:3%-5% diversity factor is acceptable.

Hot topic: Sequential valve

After about 6 month operation, we should transfer turbine to Sequential valve mode for economic efficiency.

Actually, valve arrest steam flow, decrease of the steam parameters. On condition of constant load, we try to reduce the quantity of operating GVs as possible.

In single mode, we send the total flow command to every GV. In sequential mode, there are some curves to arrange of GVs.

Single-Sequence valves cant be transferred in the turbine following boiler mode.

In order to hold the load, we tune GV lap according to the lifting curves.

Gvs Lifting Curves

Flow Distribute Curve

Total Flow-Gv Lifting

Name: ChentaoEmail: chentao@shanghai-electric.comlarrychan2005@163.com