Understanding and Verifying Compressor Safeties

Joe Pillis

Director of Industrial Refrigeration Engineering

Frick / JCI

May 2016

Why are you here ?

• Education to meet the needs of PSM, RMP, General Duty Clause

• Mechanical Integrity

• Process hazards analysis

• Preventive Maintenance Program

• RAGAGEP

PSM requirements

RAGAGEP

RAGAGEP

Foundation of safe equipment design

• Proper selection of System Design Pressure

• Relief valve installation, sizing, piping, and correct setting

• Ammonia detectors and emergency ventilation

• Limiting devices

IIAR is publishing suite of standards to establish a source of RAGAGEP forAmmonia refrigeration systems, including yearly inspection and testing.

Proper training and PPE is required for all personnel involved in testing safeties !!

• IIAR 2014 –• High stage water cooled or evap condensing - 250psig

• High stage air cooled condensing - 300 psig• Except recip. low-side could be - 250 psig

• Booster compressors and low side - 250 psig

Before we get to limiting devices:

Minimum Design Pressure

Booster minimum design pressure changed in 2014 release of IIAR-2

New additional consideration (IIAR-2) of maximum ambient, (in minimum design pressure calculation)

ambient considerations degrees

for design pressure calcs degrees Yuma Ariz fahrenheit

IIAR-2 2014 F plus 1% db F max psig

low pressure side 10 110.9 120.9 275.6

114.6 250

pensacola

1% WB psig

high pressure side WC 30 81.5 111.5 238

high pressure side evap cooled 114.6 250

DLCWT

15 85 F 100 197

250

high pressure side of air cooled 30 110.9 140.9 369.1

300

Summary of ambient considerations:

If 1% DB is over 104.6 F, low side designpressure must be above 250 psig

If 1% DB is over 96.5 F, high side designpressure must be over 300 psig

Safety relief valve (sizing) IIAR-2

Ammonia Detection (IIAR-2)

Emergency ventilation actuated

Compressor Limiting Devices (Safeties) Purpose: • To provide a safe work environment for employees, and other

personnel.

• To prevent accidental release of refrigerant

• To prevent damage to property, product, or equipment

Limiting devices (Operational safeties) IIAR-2

Critical safeties

• High discharge pressure cutout - avoid relief valve opening

• Low suction pressure cutout - avoid evaporator freeze-up or compressor damage from too high compression ratio.

• High discharge temperature cutout - avoid compressor damage

• Lubrication failure control (on systems with force feed oil) avoid compressor damage

• High liquid level in suction accumulator – avoid compressor damage

• High motor amps - avoid motor or compressor damage –(Arc flash danger, Proper PPE and training required) We do not recommend testing current cut-out.

Limiting devices can be:

• Pressure, temperature, level actuated switches.

• Transducers (Pressure, temperature, amps, kW, liquid level ) tied to a controller.

At most basic level

• High Discharge Pressure Cut Out switch (manual reset)

• Low Suction Pressure Cut Out switch

• Fuse or breaker for high amps

• Low Oil Pressure Cut Out switch (if an oil pump present)

HPCOswitch

Setting switch ranges

Early Refrig system

Early reciprocating compressors equipped with pressure switch safeties• High Pressure Cut-out, (avoid lifting relief valves)

• Low pressure Cut-out, (avoid high CR and disch temp)

• Oil pressure cut-out on compressors with oil pumps, (avoid failing compressor)

• Fuse on electric power, (over amp)

Ammonia Screw compressor with mounted starter

Frick Quantum Panel has 280 Warnings and Shutdowns as standard.

Categories of safety shutdowns

• Compressor P & T safeties (32)

• Electric Motor safeties (8)

• Starter safeties (3)

• Analog sensor fault detection (18)

• Communication safeties (5)

• Vibration monitoring safeties (4)

• Variable speed drive safeties (67)

• Engine and turbine drive safeties (4)

• ~ 140 shutdowns ~140 warnings

Compressor safeties (from P&T sensors)

High discharge pressure

High Discharge temperature

High limit discharge pressure max

High limit discharge temperature

High comp oil pressure

High comp oil temp

Low comp oil pressure

Low comp oil temperature

Low demand pump pressure

Low discharge pressure

Low Main Oil Injection pressure

Missing comp oil pressure A,B,C

High oil filter pressure differential

Balance Piston Pressure

High liquid level shutdown

High process entering temp shutdown

High process leaving temp shutdown

High suction pressure

Low suction pressure 4

Low process entering temp

Low process leaving temp

Oil Level

Oil Logging

Separator condensing liquid

Low sep temperature

Coalescing Filter Diff

Liquid Slugging

Compressor safeties (critical)

High discharge pressure

High Discharge temperature

High limit discharge pressure max

High limit discharge temperature

High comp oil pressure

High comp oil temp

Low comp oil pressure

Low comp oil temperature

Low demand pump pressure

Low discharge pressure

Low Main Oil Injection pressure

Missing comp oil pressure A,B,C

High oil filter pressure differential

Balance Piston Pressure

High liquid level shutdown

High process entering temp shutdown

High process leaving temp shutdown

High suction pressure

Low suction pressure 4

Low process entering temp

Low process leaving temp

Oil Level

Oil Logging

Separator condensing liquid

Low sep temperature

Coalescing Filter Diff

Liquid Slugging

Electric Motor safeties

False Running Fail Motor Amps high

High motor current shutdown

Low motor current

High motor stator temp 3

High motor bearing temp 2

Compressor off but amps > Low motor amp shutdown setpoint

When so equipped

Broken coupling

Vibration safeties (when so equipped)

High comp vibration suction

High comp vibration disch

High motor vibration shaft side

High motor vibration opposite shaft side

Starter safeties

compressor Aux. motor starter

compressor Start failure

starter shutdown

Starter contactor de-energized

Start not confirmed 30 sec

Start not confirmed 45 sec

Analog sensor fault safeties

High comp oil pressure sensor fault

High discharge pressure sensor fault

High discharge temperature sensor fault

High oil temp sensor fault

High kW monitoring sensor fault

High Separator temp sensor fault

High economizer pressure sensor fault

High suct temperature sensor fault

High suct pressure sensor fault

Low comp oil pressure sensor fault

Low discharge Pressure sensor fault

Low discharge Temperature sensor fault

Low compr oil temp sensor fault

Low kW monitoring sensor fault

Low sep temperature sensor fault

Low economizer pressure sensor fault

Low suct temperature sensor fault

Low suct pressure sensor fault

Most sensors will fail at max or min reading, we test for both conditions and alarm and shutdown if it appears a critical device has failed.Temperatures open – fail high.

Engine or turbine drive safeties

High manifold pressure

High rpm - eng or turbine drive

Low rpm engine or turbine drive

Start failure for eng and turbine

Variable speed drive safeties

VSD safeties 67

Current imbalance, high/low voltage faults, high and low temperatures, communication failures, instantaneous current high, logic board fault, gate driver faults, pre-charge lockout, harmonic filter safeties,…………….blah, blah, blah…

Communication safeties

Analog Comm

Digital comm

High analog value

Low aux analog

Oil pump aux not energized

Handshake between processor and all I/O boards

Testing of Critical Safeties

• High discharge pressure

• Low suction pressure

• Compressor low oil pressure

• High Discharge temperature

• High liquid level in suction accumulator

• High motor current (not recommended)

Testing and verifying safety functionASHRAE 15

• IIAR-6 will require: 1. Annual Testing

1. Perform functional test of safety shut downs1. Low suction pressure2. High discharge pressure3. High liquid level4. Low oil pressure

Most are fairly easy to test but high dischargepressure is often questioned.

Testing of critical safeties.

• A pressure limiting device may be an electro mechanical switch with manual reset, or a pressure transducer/transmitter connected to an electronic controller.

• Testing of the pressure limiting device requires proof of the three following characteristics:• Function of the device to stop the compressor.

• Set-point shall be no more than 90% of the setting of the pressure relief device protecting the high side of the system.

• Calibration of the device to show it reads, (or trips), correctly when compared to a “Pressure standard: dead weight tester, or master gauge traceable to NIST” with an up-to-date certification. (traceability requirement is not final yet)

Pressure limiting device –(High pressure cut-out)

What is a “Pressure Standard”

Dead weight pressure gauge calibrator

• Several possible test methods.

• With master gauge installed on same pressure to be tested.• Raise condensing pressure or throttle discharge valve until compressors trips, (carefully).

• Lower cutout pressure to level where easy to attain, raise condensing pressure or throttle discharge valve until compressor trips. Reset cutout pressure to normal value, not to exceed 90% of safety relief valve setting.

• Install check valve in HPCO line and use external pressure source to raise pressure until compressor trips. Stop valve not allowed in HPCO line.

High Pressure Cut-out(How to test function)

More details will be included in IIAR-6. Lowering of setpoint not yet finalized

High Pressure Cut-out(How to test function)

High Pressure Cut-outPossible calibration block

Low suction pressure cutout and low oil pressure cutout• Connect “pressure standard” to read same pressure being tested.

• Throttle suction valve or oil valve until compressor trips within required tolerance.

• If cutout pressure is outside of acceptable tolerance adjust cutout pressure and retest.

• Check pressure reading against pressure standard• Pressure gauges should read within gauge tolerance of full scale.

• Transducer reading can be offset to agree with pressure standard reading.

High discharge temperature cutout

• Remove temperature measurement probe from sealed well leaving wires in place.

• Use temperature calibrator or heated oil bath to increase temperature of probe until compressor trips within acceptable tolerance.

• Re-install probe.

• Or, drop temperature setting where trip will occur into operating range, and raise discharge temperature until cutout trips compressor, then reset trip temperature.

High motor current

• Trip is not recommended

• Check amps measured on controls against calibrated hand ammeter for accuracy, on scheduled basis.

• NOTE : Arc Flash risk. Requires training and proper PPE.

High liquid level cutout

• Liquid level sensor on suction accumulator vessel

• Generally on a float column

• Float column should have isolation valve

• Close bottom valve and fill column with liquid from pumped liquid source until compressor trips on high level.

• Confirm level is correct by visual presence of liquid in bullseye sightglass.

• Open bottom valve when complete

Disclaimer

• Advice and recommendations given in this series of slides represent the author’s opinion only and should not be construed as consulting or design guidance, nor is it sanctioned by IRC or Johnson Controls. Each company is responsible for their own safety program based on consideration of all the parameters of their own system design.

• Credit to International Institute of Ammonia Refrigeration and ASHRAE for reference paragraphs included from IIAR-2, and ASHRAE-15

• Recommended test methods are still under revision in IIAR 5 and IIAR 6. Make sure you stay up to date with published standards.

Questions