IEEE Power & Energy Magazine - May/June 2021 - 91

exports of energy, and EPS interconnections provide critical set points for exporting and importing power, response
times, and methods to validate components and systems for
listing. It is noted that these new product standards apply
to components, equipment, subsystems, and systems. One
example of a listing that includes several areas of testing and
disciplines is UL 1741, Standard for Inverters, Converters,
Controllers, and Interconnection System Equipment for Use
With Distributed Energy Resources. The UL 1741 requirements cover inverters, converters, charge controllers, and
interconnection system equipment intended for use in utility-interactive standard (grid-connected) power systems and
islanded systems. Utility-interactive inverters and converters
are typically intended to be operated while connected to an
EPS to supply power to common loads.
To illustrate some of the complexity and interplay of compatible and linked standards, utility-interactive standard equipment requirements are intended to supplement and be used in
conjunction with IEEE 1547, Standard for Interconnecting

Distributed Resources with Electric Power Systems, and IEEE
1547.1, Standard for Conformance Test Procedures for Equipment Interconnecting Distributed Resources With Electric
Power Systems. The requirements specified in UL 1741 include
✔✔ power systems that combine other alternative energy
sources with inverters, converters, charge controllers,
and interconnection system equipment in systemspecific combinations that include protection, such as
overvoltage and frequency
✔✔ products that are intended to be installed according
to the National Electrical Code (National Fire Protection Association 70) and that often require protective
devices that are considered to be protection for an interconnection or system
✔✔ references to the nearly 100 UL standards that are used
to certify hardware and software applicable to utilityinteractive inverters, protection devices, and systems.
A new UL 3001 standard is being developed that will apply
to components and systems associated with DERs and

table 3. The IEEE C37 protection-specific standard.
IEEE Standard Title
IEEE C37.1062003,
active
standard

IEEE Guide for Abnormal
Frequency Protection for
Power Generating Plants

Protection Relevance and Description

Notes

Structural category
This guide provides information for
applications of relays based on 2003
products. Updates appear to be overdue
for attention.

This guide was developed to assist
protection engineers with applying
relays for the protection of generating
plant equipment from damage caused
by operations at abnormal frequencies,
including overexcitation.

table 4. The UL standards applicable to microgrid systems and protection.
UL Standard

Title

Protection Relevance and Description

Notes

UL 1741,
active
standard

Standard for Inverters,
Converters, Controllers,
and Interconnection
System Equipment for
Use With Distributed
Energy Resources

Structural category
This standard provides specifications
for characteristics that can impact
interconnection operations and safety,
including protection settings and
operation details.

This standard is for product certification.
Certification provides operation safety
and compatibility information that can
be related to devices and processes,
including protection. This standard is
being harmonized as UL 62109 for
compatibility with IEC 62109. It is written
to be compatible with the California
Public Utility Commission Rule 21, which
focuses on smart inverter functionality.

UL 1741
Supplement A,
UL 1741
Supplement B,
active
standards

Supplement SA-
Grid support-Utility
interactive equipment
Supplement SB-
Compatibility with IEEE
1547.1

Structural category
The combined extensions of UL 1741
provide for the testing and performance
requirements of the conversion devices
used in DERs and microgrids. They
will aid in designing protection
methodologies and systems.

UL 1741-SA and UL 1741-SB add to
product safety standards that lay out
manufacturing (including software) and
product requirements for inverters that are
more capable of meeting requirements for
EPS out-of-spec excursions and improving
EPS reliability.

UL 3001,
under
development

Safety Standard for
Distributed Energy and
Storage Systems

Structural category
This a new product safety standard
for DERs and storage systems, which
are often called microgrids. Listing
systems will provide insight into the
characteristics of DER and microgrid
functionalities that facilitate protection.

UL 3001 is a listing standard that is
based on systems installed by qualified
persons following the instructions and all
applicable codes and standards. Hence, a
listed product is evaluated for safety and
selected functionality.

UL: Underwriters Laboratory.

may/june 2021

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IEEE Power & Energy Magazine - May/June 2021

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