Variable speed fire pump controllers

Variable Speed Fire Pump Controllers

- for -

F.M. Approvals- by -

James S. NasbyColumbia Engineering

C.E. F.M. Approvals 2

Topics to be CoveredVFD and Controller ElementsVFD CharacteristicsPrimary (Desired) Effects on MotorSecondary (Undesired) Effects

On MotorOn Power Grid (Mains)

System Characteristics & EffectsMotor RequirementsApplicationsTesting


Model ECV-250-46-*

250 Hp – Single Source

A.T.L Start in Bypass


Model ECVRTZ-100-46-*


Inside View of Drive Bay

D.C. Link Reactor

Line Reactor

CoolerCPT & Fuses


Vocabulary

VFD = Variable Frequency DriveAFD = Adjustable Frequency DriveVSD = Variable Speed DriveASD = Adjustable Speed Drive,“Inverters”, “A.C. Drives”, "Drive"

Note: The above are all the same for our purposes.IGBT = Insulated Gate Bipolar Transistor“VFD” will refer to the Drive Unit ProperPWM = Pulse Width ModulationdV/dt = Voltage Rise Time (dU/dt in Europe)


Vocabulary – cont’d

IGBT "Soft Switching" Reduces = dV/dt Reducing Motor Spikes (GE/Figi)PWM = Pulse Width Modulation (Used on

All Modern VFDs)PID = "Proportional – Integral –

Differential" Set Point Controller or Control Scheme


Vocabulary – cont’dInverter Duty Motor

Higher Winding Insulation Dielectric Strength (Breakdown Voltage), Typically 1200 VacExtra Thermal Capacity by way of:

1.15 Service Factor and/orHigher Insulation Class (Such as 155°C instead of 130°C)

Mitigate Bearing Currents by way of:Insulated BearingsBrushes to Drain (Bypass) Currents Around Bearings


Vocabulary – cont’d

Constant Torque Rating: For Mills and Take- up Reel Drives and Positive Displacement (Piston) Pumps

Where Rated Torque is Needed at Zero (or Near Zero) Speed.

Variable Torque Rating: For Fans, Blowers, Centrifugal Pumps & etc.

Where the Load Torque Varies with Speed (RPM). E.g.: Low Torque at Zero (and Near Zero) Speeds.


Vocabulary – cont’dSet-Point = Desired Outcome(e.g.: Desired Pressure)System Response May Be One:

OscillatoryUnder DampedCritically Damped (with or w/o Overshoot)Over Damped


System Response Curves

Under DampedOscillatory

(With Overshoot)Over DampedCritically Damped


Required Controller ElementsController Must be a Full Service Controller

Plus a VFD UnitPlus VFD Fuses (at <299% of FLA)Plus Load Side Isolation Contactor (interlocked)Plus Line Side Isolation ContactorPlus By-Pass (Main) Contactor

All Fully Rated (Horsepower Rated)Line Reactor - 5% Minimum to:

Reduce Line Current HarmonicsReduce Line Transients to the VFDReduce Capacitor Over-voltage Shutdown due to Line Spikes and/or Surges

Note: All line spikes and surges get rectified regardless of where they appear on the Waveform.


Required Controller Elements - cont'd

Mechanical Interlock Between Bypass Contactor and VFD Output Contactor to

Prevent Back Feeding VFD on Controller Defect since this will cause the Main Fire Pump Circuit Breaker (C/B) to Trip. This causes the Fire Pump to be off line (dead).

Means to Lock VFD and Starting ParametersTypical VFD has over 150 settable parameters, many of which will cause damage or no fire water if mis-set

PID to Control PressureMust be able to Control Time Constants and Dynamic Characteristics to Avoid Cycling or Hydraulic System Damage


Power Circuit Schematic

* Was Optional


VFD OCP Fuses and view of VFD Sans Cover


Schematic Diagram

Single SourceA.T.L. (D.O.L.)Starting in Bypass ModeLow to ModerateHorsepower

Note Mechanical Interlock (Mech Intk) Between R1 and BP Contactors.


Line Reactor and 2nd Cooler


Two Coolers for 300 Hp VFD

Note: this unit sees regular service a pump company pump test facility.


Must Include a Complete Full Service Fire Pump Controller

Standard Full Service Circuitry and ComponentsStandard Mechanical Manual OperatorMode Switch for Full Speed Bypass Operation

Easier Commissioning, Servicing and for Back-up Automatic Fire Protection

Standard Pressure Switch/TransducerBypass and Start use the Same Switch -or-

Separate Swtiches used (some Mfrs)Separate (2nd) Transducer for Recording (one Mfr.)


Close-up of Pressure Switch and Both Pressure Transducers


External Wiring Diagram


Optional Controller Elements

Line Side EMI / RFI (EMC) FilterLoad Side (Motor) Output ReactorLoad Side (Motor) dV/dt FilterD.C. Link Reactor (Standard with Some)

Advanced Operator Display PanelsNetwork Connection


VFD – Principles of Operation

Three Main Sections:Three Phase Rectifier Section (AC/DC)D.C. Filter Section - D.C. Bus Capacitors (Bus Cap’s)Inverter Section (DC/AC): Pulse Width Modulator (PWM)Modern VFD’s use IGBT’s for InverterInverter Typically Runs at 2 to 6 Kilohertz


VFD = Motor Running Only (No Motor Starting Region)

Typical Motor Torque and Pump Torque Curves


Lower Frequency Shortens CurveThis point Moves Left Relative to Frequency

100% = 60 Hz or 59 or 30 or any Frequency


3 PhaseLine Freq.

AC / DC

Smoothing

DC / ACAt “X” Khz

VFD – Principles of Operation

Modulation Frequeny Typically 2 to 10 Khz


PWM Basic VFD Voltage Waveform Pulse Mode Modulation at 2.0 to 10.0 Khertz

2 Khz

One Cycle


PWM Motor Voltage Waveform with No Filtering


PWM Motor Voltage Waveform with Load (Motor) Reactor


PWM Motor Voltage Waveform with Motor Filter


Motor Electrical MeasurementsSpecial Metering Required due to the High Voltage and Frequency


Controller Operation1) Pressure Switch Trips2) Contactor R1 and R2 Close3) Signal VFD to Start4) Begin Timing for VFD Ready Signal(3-5 Sec.)

5) Begin Pressure Switch Tripped Timing (approx. 20 Seconds)

6) VFD Sends “Drive Ready” Signal -or-


Controller Operation – cont’d7) Bypass Operation Begins after Restart Delay

-- or --8) VFD Begins Motor Acceleration9) VFD adjust motor speed to Achieve Desired

Pump Pressure Set-Point10) Pump Builds Up Sufficient Pressure to Reset

the Pressure Switch within 20 Seconds -or-

11) Begin Bypass Operation (Same as # 7 above)


Controller Operation – cont’d12) VFD Modulates Motor Speed Using its PID

to Maintain System Pressure at Desires Set- Point Even with Flow and Suction Pressure Fluctuations -or-

13) Pressure Switch Re-Trips and Pressure Switch Tripped Timer Begins Timing Cycle (Again)

14) After 20 Seconds, By-Pass Operation Begins (same as #7 above)

15) By-Pass Operation is Manual Reset


Bypass Starting Methods

Full Voltage (A-T-L)Primary ReactorSoft StarterSome Controllers also Provide Soft Stop(extra circuitry needed for the Soft Stop Function)Some Units will Ramp Up to at Lease an Idle Speed and continue to increase speed until the pressure demand is met.


VFD Starting CharacteristicsAll VFDs provide Soft Starting (Ramp-up)Max. Torque/Current can be set

150% Starting and 110% Running are TypicalSystem Must be Suitable for Bypass Mode Starting

Some Controllers also Provide Soft Stop(extra circuitry needed for the Soft Stop Function)Some Units will Ramp Up to at Lease an Idle Speed and continue to increase speed until the pressure demand is met.


Design Considerations

Capacitor Overvoltage ShutdownThis is a Lockout Condition, Manual Reset is always Required.480 Vac x 1.414 = 678 + 10% = 747 Vac. Better VFD'sdon't shut down until the capacitor voltage exceeds 800 Vac. Lesser ones shutdown at 750 Vac or less.

VFD Shutdown Temperature.Better VFDs don't shutdown until 70ºC and can be restarted with no damage or degradation

VFD Pollution Degree Requirements must be met.Cooling should be Closed Loop (no Venting Pump Room Air into Controller.


Design Considerations - cont'dVFD OCP Must be Fully Selectively Coordinated with the Main Fire Pump Circuit Breaker (C/B)

Said OCP will Most Likely be FusesCoordination with the is Critical to Avoid Tripping which Kills the Bypass Mode.Fuses (OCP) must trip before the 300% pointFuses must trip in less than 8 seconds at Locked Rotor CurrentFuses must still be large enough to hold with the Maximum normal VFD input current including harmonic content.The Fuse curve must never touch the C/B curve to avoid any risk of tripping.Fuse tolerance must also be considered. The plus tolerance on the fuse curve can lead to tripping of the F.P. C/B.


Design Considerations - cont'dFuses must be calculated for Each and Every controller Hp and Voltage (E.g.: Each nominal FLA).Controller cooling must keep the VFD within is maximum rated temperature.

A 50ºC VFD will require the cooling to keep the temperature rise to no more than 10ºC for a Controller Rated Maximum Temperature of 40ºC.A VFD rated at only 40ºC will require de-rating unless refrigeration is allowed.


Design Considerations - cont'dPolution Degree Rating of the VFD must not be exceeded. This will typically require a non- vented NEMA 12 (U.L. Type 12) or better enclosure and cooling means. Internal Controller Wiring in the VFD input path must be sized for the harmonic content of the VFD.Successful Installations the Mfr. to ascertain and check the system hydraulic time constants and set the PID parameters accordingly.


Application ConsiderationsAdditional Considerations:

* The controller is UL listed for fire pump applications.* The enclosure is rated for NEMA 12.* Maximum ambient must not exceed controller (marked) rating. * Mfr's vent air clearance spaces and service spaces must be adheared to. * The motor must be suitable for use with a variable speed drive.* Motor current draw must not exceed 100% of FLA, even though the motor

may have a 1.15 or higher service factor* A gen-set must be suitable for use with a variable speed drive.* The power source must be capable of bypass mode Starting method.* The pump and motor must be rigidly coupled.* The pump and motor must be properly grouted.* A relief valve is required for emergency operation unless system pressure

can not be exceed at churn and full speed and max. suction pressure.


Multi-Acre Multi- Building Campus …


…and Back-up Distant Water Supply…


Lead to Multiple System Time Constants

Note

253 Second

Chart Span


Note 151 Sec.

Chart Span



Note 86 Sec.

Chart Span



Note 63 Sec.

Chart Span


Estimated 25s, 20s, 4s, 2s & ?? Hydraulic Time Constants


Unit Testing

Small Unit after High and Low Temp. Testing:

Ta < 0ºC and

Ta > 60ºC

Thermocouple Switch Box on top of unit.


Unit Testing


Unit Testing - 350 Hp Unit

Questions?

Variable speed fire pump controllers

Engineering

Transcript of Variable speed fire pump controllers