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aka: Using the latest code changes to improve system reliability… and maybe even save some $$$....
2018 Annual Conference
Optimizing Emergency Power Systems for Health Care Applications
▶ Michigan currently utilizes 2014 National Electrical Code (NEC) with a few amendments ▪ Amendments don’t affect this discussion▪ Some interesting changes in 2017 NEC will also be covered
▶ Health Care facilities with emergency generator powered loads must comply with NFPA 110 Level 1 requirements (2013)
Overview
▶ 2014 required marking on the generator set; 2017 softens it by allowing “instructions”
▶ Provides a means to verify available fault current from the alternator
▶ Allows designer to verify that what was specified and promised is supplied
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Generator Labeling Requirements445.11 Marking (2017). Each generator shall be provided with a nameplate giving the manufacturer’s name, the rated frequency, the number of phases if ac, the rating in kilowatts or kilovolt-amperes, the power factor, the normal volts and amperes corresponding to the rating, the rated ambient temperature, and the rated temperature rise.Nameplates or manufacturer’s instructions shall provide the following information for all stationary generators and portable generators rated more than 15 kW
(1) Subtransient, transient, synchronous, and zero sequence reactances
(2) Power rating category(3) Insulation system class(4) Indication if the generator is protected against overload by
inherent design, an overcurrent protective relay, circuit breaker, or fuse
(5) Maximum short circuit current for inverter-based generators, in lieu of the synchronous, subtransient, and transient reactances
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More Labeling445.11(cont’d—new in 2014)Marking shall be provided by the manufacturer to indicate whether or not the generator neutral is bonded to the generator frame. Where the bonding of a generator is modified in the field, additional marking shall be required to indicate whether the generator neutral is bonded to the generator frame.
▶ Bonding practice is not standardized between manufacturers
▶ Designers should:▪ State requirements on system 1-line▪ Generally:⚫ If ground fault is required on any circuit upstream from
an ATS, 4-pole ATS required (4-wire systems)⚫ If 4-pole ATS, bond at generator or where conductors
from generator enter the building⚫ If 3-pole/4-wire, bond must be at utility source service
entrance and generator cannot have bond at generator▪ One N-G bond on any neutral bus…
SSwitched neutral
2017 Change:700.6(D) Ground Fault. …For systems with multiple emergency sources connected to a parallel bus, the ground fault sensor shall be permitted to be in an alternative location.
Also allowed in article 701 and 702 systems—in other words: all systems…
For multiple generator 4-wire system bond at neutral bus!
▶ Thermal Damage Characteristics (low Z fault) ▪ Alternator is more susceptible to damage than fully
rated conductors⚫ NEMA MG1 requires I2t = 40 basis unless tested to validate
different value⚫ End point is based on X”d▪ Time to damage depends on the nature of the fault⚫ Secondary damage due to overvoltage on single phase faults⚫ Single phase faults usually require faster tripping
▪ Generator submittals should include thermal damage information and demonstrate protection provided
▶ Electrical evaluation does not consider mechanical integrity of alternator and engine▪ Must use prototype testing to validate design per NFPA
110
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Alternator Protection
▶ Notice:▪ All generators have similar damage curves⚫ Biggest difference is end point of curve (defined by X”d)
▪ A generator can’t make enough fault current to damage itself in less than:
⚫ 8-10 seconds for a 3-phase fault⚫ As little as 1 second on a single phase fault⚫ Instantaneous trips never needed
▪ A generator can’t damage a fully rated conductor set when it is properly protected
⚫ A reason why NEC does not require cb at genset…▪ Single phase faults have a higher probability of alternator
damage than 3-phase faults⚫ NEED overvoltage protection, properly set⚫ Trip relatively quickly, but not so quick as to nuisance trip on
normally occurring conditions
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Alternator Protection
▶ Latest control systems from major US genset suppliers incorporate integrated protection specifically designed to protect the alternator▪ Least risk to designer/owner as failure to protect the generator is
responsibility on must incorporate a listing label ▪ Verify listing at submittal using file number at
ul.com/certification directory
▪ UL Certification directory describes listing details & requirements:
⚫ Category (FTPM or NRGU may be used)⚫ Installation requirements vary with category and listing
▶ 2017 NEC requires a label describing alternator protection (implied in previous versions)▪ When proper alternator protection is provided no other
protection is required for a fully rated feeder
▶ “Masterspec” text is generally not adequate to assure proper generator protection
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Protecting a Generator Set
Disconnect Means with Lock-out/Tag-out ▶ Article 445.18 – Generators shall be equipped with disconnect(s), lockable in
the open position, by means of which the generator and all protective devices and control apparatus are able to be disconnected entirely for the circuits supplied by the generator except where both of the following conditions apply:
1) The driving means for the generator can be readily shut down, is rendered incapable of restarting, and is lockable in the OFF position in accordance with 110.25. (2014 change).
2) The generator is not arranged to operate in parallel with another generator or other source of voltage.
▶ Article 700.12.B (6) -- Where an outdoor housed generator set is equipped with a readily accessible disconnecting means located within sight of the building or structure supplied, an additional disconnecting means shall not be required where ungrounded conductors serve or pass through the building or structure. The disconnecting means shall meet the requirements of 225.36.
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Per 700.16, location of disconnect for emergency circuits is required to be illuminated…
2017 change
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445.18 Disconnecting Means and Shutdown of Prime Mover. (A) Disconnecting Means. Generators other than cord and plug-connected portable shall have one or more disconnecting means. Each disconnecting means shall simultaneously open all ungrounded conductors. Each disconnecting means shall be lockable in the open position in accordance with 110.25.(B) Shutdown of Prime Mover. Generators shall have provisions to shut down the prime mover. The means of shutdown shall comply with all of the following:(1) Be equipped with provisions to disable all prime mover start control circuits to render the prime mover incapable of starting.(2) Initiate a shutdown mechanism that requires a mechanical reset.The provisions to shut down the prime mover shall be permitted to satisfy the requirements of 445.18(A) where it is capable of being locked in the open position in accordance with 110.25.Generators with greater than 15kW rating shall be provided with an additional requirement to shut down the prime mover. This additional shutdown means shall be located outside the equipment room or generator enclosure and shall meet the requirements of 445.18 (B)(1) and (B)(2).
Disconnects for Outdoor Gensets
▶ Most generator set installations will require the use of a disconnect device where the conductors “enter the building or structure”.▪ Exceptions possible on sites with single
management, qualified personnel for operation, and documented procedures
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700.12 (B) (6) Outdoor Generator Sets. Where an outdoor housed generator set is equipped with a readily accessible disconnecting means in accordance with 445.18, and the disconnecting means is located within sight of the building or structure supplied, an additional disconnecting means shall not be required where ungrounded conductors serve or pass through the building or structure…
SUSE Breaker or Connection Box Requirements
Ground BusElectrically solid to alternator frame & genset frame
Neutral to Ground Link
Ground Fault Provisions
Adequate Lug Space
Required LabelsUL, Protection, Etc.
Wire Bend Space(Top or Bottom Connect)
Bracing & Spacing
Supply Side Barriers for SUSE (Not Shown)
NEC requires disconnects to be suitable for use as service equipment (700.12 B (6))
2014 NEC does not require all these provisions when disconnect is on genset.
Should circuit breakers be installed on generator sets?▶ We have seen that:
▪ Circuit breakers generally don’t provide required alternator protection
⚫ Generators can provided with breakers as a listed assembly, but UL doesn’t verify that they actually protect the alternator
⚫ NEC specifically allows other options
⚫ Environmental issues with CB’s
▪ Circuit breakers are not required to meet generator disconnect requirements
⚫ For outdoor generator installations they generally don’t meet the “within sight” rule as installed
⚫ You probably need one or more “where the conductors enter the building or structure”
▪ Coordination for emergency systems can be difficult with multiple breaker manufacturers
⚫ Less of an issue for essential electrical systems (0.1 S rule)
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445.12 (A) Constant-Voltage Generators. Constant-voltage generators, except ac generator exciters, shall be protected from overload by inherent design, circuit breakers, fuses, protective relays, or other identified overcurrent protective means suitable for the conditions of use. (2011, 2014 & 2017)
445.13 (B) Overcurrent Protection Provided. Where a generator set is protected with a listed overcurrent protective device or a combination of a current transformer and protective relay conductors shall be allowed to be tapped from the load side of the protected terminals in accordance with 240.21(B). (2017)
700.10(B) (5) (b) Exception:Exception to (5)b: Overcurrent protection shall be permitted at the source or for the equipment, provided that the overcurrent protection complies with the requirements of 700.28. (requires selective coordination)
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Impact of NEC Tap Rules
See 517.30(F)
▶ Intended to allow a qualified designer to make judgements on the best way to meet the objectives of selective coordination…
▶ Applies to any system
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Here’s one that might make you smile…
700.32 Selective Coordination.Emergency system(s) overcurrent devices shall be selectively coordinated with all supply-side overcurrent protective devices. Selective coordination shall be selected by a licensed professional engineer or other qualified persons engaged primarily in the design, installation, or maintenance of electrical systems. The selection shall be documented and made available to those authorized to design, install, inspect, maintain, and operate the system.
▶ Requires a change to the decades old practices of using a normally open contact that closes to start a generator.▪ Most suppliers looking at going to a NC contact that opens.⚫ How do you deal with multiple switches?▪ What do you do about the non-emergency transfer switches?⚫ No requirement that limits use of a NC to emergency
▶ Requires additional alarm lamps in the remote annunciator—indicators for each emergency ATS and fire pump ATS▪ Specs need updating
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2017 “Failsafe” Starting & Alarming
▶ New for 2017: Start circuit from fire pump and emergency ATS to generator set must be continuously monitored, and be “fail safe”
▶ Same rules apply to emergency circuits▶ Fire pump power conductors from a generator should be
protected for short circuit, and are not allowed to have overload protection▪ Generators are required to be protected; but conductors
from generator have only overload protection (remember, gensets can’t damage themselves in less than 1 sec.)
▪ Best practice is to have listed protection for the generator and use tap rules in compliance to 695.6 (A) (2)
▪ Note that generator sets serving fire pumps, and the fire pump circuit can’t have ground fault trips 695(G).
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Fire Pump Applications
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2017 Provisions for Temporary Source700.16 Temporary Source of Power for maintenance or repair of the Alternate Power Source. …The permanent switching means to connect a portable or temporary or alternate source of power shall comply with the following: 1. Connection to the portable or temporary source shall not
require modification of permanent system wiring2. Transfer of power shall be in accordance with 700.12.3. The connection point for the portable or temporary alternate
source shall be marked with phase rotation and system bonding requirements.
4. Mechanical or electrical interlocking shall prevent interconnection of power sources.
5. The switching source shall include a contact point that shall annunciate at a location remote from the generator or at another facility monitoring system that the permanent emergency power source is disconnected from the emergency system.
Motivation: • Time required to make temporary connections and, • Deterioration of connection points for feeders
Figure 700.3(F)
▶ 700.3(F)(1) requires that connection to a load bank be done without disturbing normal power connections.▪ Easy way to do that is to have a dedicated load
bank connection⚫ On the generator or remote from the generator at an
accessible location⚫ Should trip if normal power fails while on load bank
▪ Some suppliers are building a combination of load bank and manual ATS into one box.
▪ Remember to locate field connections in an accessible location
▶ Good idea for any critical generator installation
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2017 Permanent Load Bank Connection
▶ 2017 requirements for permanent provisions for both a temporary generator and a load bank connection (unless a load bank is permanently connected to genset. ▪ Load bank should accept trip signal if
genset gets a remote start or if desired, if genset is overloaded.
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▶ Same functions using interlocked circuit breaker design
▶ Mixed Blessing Design▪ Nice to have a “canned”
solution▪ BUT, ⚫ Breakers need to coordinate with
downstream for emergency, legally required, fire pumps
⚫ Breakers aren’t particularly good switches
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▶ Many outdoor generator sets don’t incorporate lighting, and if the genset disconnect is in the building, it is often also not in an area that is lighted
▶ Best practice is to have emergency lighting in the enclosure of an outdoor generator, and in the area where the generator disconnect is located.
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2017 Disconnect Illumination
700.16 …Where an emergency system is installed, emergency illumination shall be provided in the area of the disconnecting means required by 225.31 and 230.70, as applicable, where the disconnecting means are installed indoors.Exception: Alternative means that ensure that the emergency lighting illumination level is maintained shall be permitted.
▶ Requirements covering the performance of emergency and standby power systems (gensets, ATS, and switchgear) providing an alternate source of electrical power to loads in buildings and facilities in the event that the primary power source fails.
▶ Covers installation, maintenance, operation, and testing requirements as they pertain to the performance of the emergency power supply system (EPSS).
▶ Intent of standard is to achieve maximum system reliability
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NFPA 110 (2013)
▶ Proper System Design▶ Prototype Testing▶ Factory Testing▶ Field Testing▶ In-Service Testing
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Achieving Reliability
If you do these things well, you will get the best reliability!
▶ Class - minimum time, in hours, for which the EPSS is designed to operate at its rated load without being refueled or recharged.
▶ Type - maximum time that the EPSS will permit the load terminals of the transfer switch to be without acceptable electrical power.
▶ Level - two levels of equipment installation, performance, and maintenance.▪ Level 1 systems shall be installed where failure of the equipment to perform
could result in loss of human life or serious injuries▪ Level 2 systems shall be installed where failure of the EPSS to perform is less
critical to human life and safety
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Basics & Terminology
Prototype Test Requirements
Manufacturer of genset must certify compliance– All manufacturers in North America do this…
Bad news: There’s no common agreement on detailed requirements for prototype test– Designer MUST interpret requirements – What is reasonable, required, appropriate to needs of the application?
▶ Critical, and often not careful enough▪ Objectives: verify that machine is built correctly and performs as well
or better than prototype▪ Provides data to verify field installation is proper
▶ Recommended Required testing ▪ Complete standard production testing▪ Cold start test (engine warm but not at operating temp)▪ 2-hour full load test (0.8 pf), recording data continuously▪ Transient tests at quarter load steps with recordings▪ Test engine protection equipment
▶ Certified test report with all data recordings
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Factory Testing
▶ Follow NFPA 110 Requirements▪ Installation of equipment is complete▪ Genset is in “cold start” condition (coolant heaters running)▪ Simulate power failure at a transfer switch, observe proper system operation with genset starting
and accepting load⚫ Be sure to record all data throughout test
⚫ Apply expected load for at least 1.5 hours
⚫ Remove start signal and observe proper system operation▪ Conduct full load test
⚫ 30% of rated load for 30 minutes, then 50% for 30 minutes, and finally 100% for 60 minutes (at 0.8 pf if not tested at 0.8 in the factory)
⚫ Record data at 15 minute intervals throughout the test▪ Cycle crank test
▪ Test engine safeties if not tested at the factory
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Initial Field Testing
▶ NFPA 110 requirements for Level 1 systems▪ Record-keeping required and is critical▪ Inspect equipment weekly using manufacturer’s inspection list or NFPA110
recommendation▪ Test with load once per month for at least 30 minutes⚫ Minimum 30% load or recommended exhaust temperature
⚫ If this can’t be met, can do annual test at 50% for 30 min. & 75% for an hour⚫ TEST ATS equipment, too▪ Test once every 36 months for duration of assigned Class (up to 4 hours)⚫ Test requires switching of loads to genset(s), Minimum 30% load for 3 hours and one
hour at 75%
▶ Best practice is to test annually at full load for at least 2 hours…using a load bank if necessary
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Regular Testing & Maintenance
▶ Objective is to verify that the system will deliver power to loads as designed
▶ NFPA 110 requirements have been “softened” over the years…we recommend being more demanding
▶ Requirements:▪ Verify each ATS will start the generator system▪ Generator will start and pick up loads within 10 seconds▪ Generator set will carry system loads
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Field Testing
▶ Inadequate prototype testing▪ No total genset short circuit testing▪ No total genset endurance testing▪ Adequate transient performance▪ Use of torsional calculations rather than testing▪ Inadequate Cooling system testing
▶ Standard factory testing▶ NETA testing that is unnecessary and potentially damaging
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Common Shortcomings
▶ Show the planned bonding for the generator neutral on every project, and remember: ONLY ONE N-G BOND ON NEUTRAL CONDUCTORS▪ For outdoor gensets, best location for N-G bond is where conductors enter building
▶ Required alternator protection can be done with any listed device; and circuit breakers generally don’t protect generators▪ Use listed and labeled protection from genset supplier
▶ Disconnect requirements can be met using E-stop▪ For outdoor generators use remote CB in building rather than mount on genset
▶ 2017 requirements for permanent load bank and temporary generator connections are a very good idea, even when they’re not required.
▶ Design, install, test and maintain systems per NFPA 110 Level 1 requirements▪ Especially prototype testing and in-service testing
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Big Things to take back to work…
