(a) Purpose. The purpose of this section is to describe the
requirements and procedures for safe and effective connection and operation
of distributed generation.
  (1) A customer may operate 60 Hertz (Hz), three-phase or single-phase
generating equipment, whether qualifying facility (QF) or non-QF, in parallel
with the utility system pursuant to an interconnection agreement, provided
that the equipment meets or exceeds the requirements of this section.
  (2) This section describes typical interconnection requirements.
Certain specific interconnection locations and conditions may require the
installation and use of more sophisticated protective devices and operating
schemes, especially when the facility is exporting power to the utility system.

  (3) If the utility concludes that an application for parallel
operation describes facilities that may require additional devices and operating
schemes, the utility shall make those additional requirements known to the
customer at the time the interconnection studies are completed.
  (4) Where the application of the technical requirements
set forth in this section appears inappropriate for a specific facility, the
customer and utility may agree to different requirements, or a party may petition
the commission for a good cause exception, after making every reasonable effort
to resolve all issues between the parties.
(b) General interconnection and protection requirements.
  (1) The customer's generation and interconnection installation
must meet all applicable national, state, and local construction and safety
codes.
  (2) The customer's generator shall be equipped with protective
hardware and software designed to prevent the generator from being connected
to a de-energized circuit owned by the utility.
  (3) The customer's generator shall be equipped with the
necessary protective hardware and software designed to prevent connection
or parallel operation of the generating equipment with the utility system
unless the utility system service voltage and frequency is of normal magnitude.

  (4) Pre-certified equipment may be installed on a company's
utility systems in accordance with an approved interconnection control and
protection scheme without further review of their design by the utility. When
the customer is exporting to the utility system using pre-certified equipment,
the protective settings and operations shall be those specified by the utility.

  (5) The customer will be responsible for protecting its
generating equipment in such a manner that utility system outages, short circuits
or other disturbances including zero sequence currents and ferroresonant over-voltages
do not damage the customer's generating equipment. The customer's protective
equipment shall also prevent unnecessary tripping of the utility system breakers
that would affect the utility system's capability of providing reliable service
to other customers.
  (6) For facilities greater than two megawatts (MW), the
utility may require that a communication channel be provided by the customer
to provide communication between the utility and the customer's facility.
The channel may be a leased telephone circuit, power line carrier, pilot wire
circuit, microwave, or other mutually agreed upon medium.
  (7) Circuit breakers or other interrupting devices at
the point of common coupling must be capable of interrupting maximum available
fault current. Facilities larger than two MW and exporting to the utility
system shall have a redundant circuit breaker unless a listed device suitable
for the rated application is used.
  (8) The customer will furnish and install a manual disconnect
device that has a visual break that is appropriate to the voltage level (a
disconnect switch, a draw-out breaker, or fuse block), and is accessible to
the utility personnel, and capable of being locked in the open position. The
customer shall follow the utility's switching, clearance, tagging, and locking
procedures, which the utility shall provide for the customer.
(c) Prevention of interference. To eliminate undesirable interference
caused by operation of the customer's generating equipment, the customer's
generator shall meet the following criteria:
  (1) Voltage. The customer will operate its generating equipment
in such a manner that the voltage levels on the utility system are in the
same range as if the generating equipment were not connected to the utility's
system. The customer shall provide an automatic method of disconnecting the
generating equipment from the utility system if a sustained voltage deviation
in excess of +5.0 % or -10% from nominal voltage persists for more than 30
seconds, or a deviation in excess of +10% or - 30% from nominal voltage persists
for more than ten cycles. The customer may reconnect when the utility system
voltage and frequency return to normal range and the system is stabilized.

  (2) Flicker. The customer's equipment shall not cause
excessive voltage flicker on the utility system. This flicker shall not exceed
3.0% voltage dip, in accordance with Institute of Electrical and Electronics
Engineers (IEEE) 519 as measured at the point of common coupling.
  (3) Frequency. The operating frequency of the customer's
generating equipment shall not deviate more than +0.5 Hertz (Hz) or -0.7 Hz
from a 60 Hz base. The customer shall automatically disconnect the generating
equipment from the utility system within 15 cycles if this frequency tolerance
cannot be maintained. The customer may reconnect when the utility system voltage
and frequency return to normal range and the system is stabilized.
  (4) Harmonics. In accordance with IEEE 519 the total harmonic
distortion (THD) voltage shall not exceed 5.0% of the fundamental 60 Hz frequency
nor 3.0% of the fundamental frequency for any individual harmonic when measured
at the point of common coupling with the utility system.
  (5) Fault and line clearing. The customer shall automatically
disconnect from the utility system within ten cycles if the voltage on one
or more phases falls below - 30% of nominal voltage on the utility system
serving the customer premises. This disconnect timing also ensures that the
generator is disconnected from the utility system prior to automatic re-close
of breakers. The customer may reconnect when the utility system voltage and
frequency return to normal range and the system is stabilized. To enhance
reliability and safety and with the utility's approval, the customer may employ
a modified relay scheme with delayed tripping or blocking using communications
equipment between customer and company.
(d) Control, protection and safety equipment requirements specific
to single phase generators of 50 kilowatts (kW) or less connected to the utility's
system. Exporting to the utility system may require additional operational
or protection devices and will require coordination of operations with the
host utility. The necessary control, protection, and safety equipment specific
to single-phase generators of 50 kW or less connected to secondary or primary
systems include an interconnect disconnect device, a generator disconnect
device, an over-voltage trip, an under-voltage trip, an over/under frequency
trip, and a synchronizing check for synchronous and other types of generators
with stand- alone capability.
(e) Control, protection and safety equipment requirements specific
to three-phase synchronous generators, induction generators, and inverter
systems. This subsection specifies the control, protection, and safety equipment
requirements specific to three phase synchronous generators, induction generators,
and inverter systems. Exporting to the utility system may require additional
operational or protection devices and will require coordination of operations
with the utility.
  (1) Three phase synchronous generators. The customer's generator
circuit breakers shall be three-phase devices with electronic or electromechanical
control. The customer is solely responsible for properly synchronizing its
generator with the utility. The excitation system response ratio shall not
be less than 0.5. The generator's excitation system(s) shall conform, as near
as reasonably achievable, to the field voltage versus time criteria specified
in American National Standards Institute Standard C50.13-1989 in order to
permit adequate field forcing during transient conditions. For generating
systems greater than two MW the customer shall maintain the automatic voltage
regulator (AVR) of each generating unit in service and operable at all times.
If the AVR is removed from service for maintenance or repair, the utility's
dispatching office shall be notified.
  (2) Three-phase induction generators and inverter systems.
Induction generation may be connected and brought up to synchronous speed
(as an induction motor) if it can be demonstrated that the initial voltage
drop measured on the utility system side at the point of common coupling is
within the visible flicker stated in subsection (c)(2) of this section. Otherwise,
the customer may be required to install hardware or employ other techniques
to bring voltage fluctuations to acceptable levels. Line-commutated inverters
do not require synchronizing equipment. Self-commutated inverters whether
of the utility-interactive type or stand-alone type shall be used in parallel
with the utility system only with synchronizing equipment. Direct-current
generation shall not be operated in parallel with the utility system.
  (3) Protective function requirements. The protective function
requirements for three phase facilities of different size and technology are
listed below.
    (A) Facilities rated ten kilowatts (kW) or less must have an
interconnect disconnect device, a generator disconnect device, an over-voltage
trip, an under-voltage trip, an over/under frequency trip, and a manual or
automatic synchronizing check (for facilities with stand alone capability).

    (B) Facilities rated in excess of 10 kW but not more than 500
kW must have an interconnect disconnect device, a generator disconnect device,
an over- voltage trip, an under-voltage trip, an over/under frequency trip,
a manual or automatic synchronizing check (for facilities with stand alone
capability), either a ground over-voltage trip or a ground over-current trip
depending on the grounding system if required by the company, and reverse
power sensing if the facility is not exporting (unless the generator is less
than the minimum load of the customer).
    (C) Facilities rated more than 500 kW but not more than 2,000
kW must have an interconnect disconnect device, a generator disconnect device,
an over- voltage trip, an under-voltage trip, an over/under frequency trip,
either a ground over-voltage trip or a ground over-current trip depending
on the grounding system if required by the company, an automatic synchronizing
check (for facilities with stand alone capability) and reverse power sensing
if the facility is not exporting (unless the facility is less than the minimum
load of the customer). If the facility is exporting power, the power direction
protective function may be used to block or delay the under frequency trip
with the agreement of the utility.
    (D) Facilities rated more than 2,000 kW but not more than 10,000
kW must have an interconnect disconnect device, a generator disconnect device,
an over- voltage trip, an under-voltage trip, an over/under frequency trip,
either a ground over-voltage trip or a ground over-current trip depending
on the grounding system if required by the company, an automatic synchronizing
check and AVR for facilities with stand alone capability, and reverse power
sensing if the facility is not exporting (unless the facility is less than
the minimum load of the customer). If the facility is exporting power, the
power direction protective function may be used to block or delay the under
frequency trip with the agreement of the utility. A telemetry/transfer trip
may also be required by the company as part of a transfer tripping or blocking
protective scheme.
(f) Facilities not identified. In the event that standards
for a specific unit or facility are not set out in this section, the company
and customer may interconnect a facility using mutually agreed upon technical
standards.
(g) Requirements specific to a facility paralleling for sixty
cycles or less (closed transition switching). The protective devices required
for facilities ten MW or less which parallel with the utility system for 60
cycles or less are an interconnect disconnect device, a generator disconnect
device, an automatic synchronizing check for generators with stand alone capability,
an over-voltage trip, an under-voltage trip, an over/under frequency trip,
and either a ground over-voltage trip or a ground over-current trip depending
on the grounding system, if required by the utility.
(h) Inspection and start-up testing. The customer shall provide
the utility with notice at least two weeks before the initial energizing and
start-up testing of the customer's generating equipment and the utility may
witness the testing of any equipment and protective systems associated with
the interconnection. The customer shall revise and re-submit the application
with information reflecting any proposed modification that may affect the
safe and reliable operation of the utility system.
(i) Site testing and commissioning. Testing of protection systems
shall include procedures to functionally test all protective elements of the
system up to and including tripping of the generator and interconnection point.
Testing will verify all protective set points and relay/breaker trip timing.
The utility may witness the testing of installed switchgear, protection systems,
and generator. The customer is responsible for routine maintenance of the
generator and control and protective equipment. The customer will maintain
records of such maintenance activities, which the utility may review at reasonable
times. For generation systems greater than 500 kW, a log of generator operations
shall be kept. At a minimum, the log shall include the date, generator time
on, and generator time off, and megawatt and megavar output. The utility may
review such logs at reasonable times.
(j) Metering. Consistent with Chapter 25, Subchapter F of this
title (relating to Metering), the utility may supply, own, and maintain all
necessary meters and associated equipment to record energy purchases by the
customer and energy exports to the utility system. The customer shall supply
at no cost to the utility a suitable location on its premises for the installation
of the utility's meters and other equipment. If metering at the generator
is required in such applications, metering that is part of the generator control
package will be considered sufficient if it meets all the measurements criteria
that would be required by a separate stand alone meter.


Source Note: The provisions of this §25.212 adopted to be effective December 21, 1999, 24 TexReg 11300