Chapter 4: Operating Characteristics (Enhanced)

Note: This page provides enhanced content for Chapter 4, including visual representations of Fault Ride Through requirements, Frequency Response characteristics, and detailed harmonic limit tables. This supplements the base Chapter 4 content.

4.4 Fault Ride Through (FRT) Capability

All MSDG installations shall have fault ride through capability as per the Grid Code requirements. The generating unit shall remain connected to the system during and after voltage disturbances.

Figure 2: Fault Ride Through (Voltage vs Time)

FAULT RIDE THROUGH REQUIREMENTS

MSDG shall remain connected within the shaded area

100%
90%
80%
70%
60%
50%
40%
25%
0%
Voltage (% of nominal)
0
0.15s
0.5s
1.5s
3.0s
Time (seconds)
REMAIN CONNECTED (Fault Ride Through) MAY TRIP 25% @ 0.15s 80% @ 0.15s 80% @ 1.5s

Fault Ride Through Requirements:

  • Point A (0.15s, 25%): For voltage drops to 25% of nominal, MSDG must remain connected for at least 0.15 seconds
  • Point B (0.15s, 80%): Between 0-0.15s, MSDG must withstand voltage down to 25% and recover to remain connected at 80%
  • Point C (1.5s, 80%): For voltage between 80-100%, MSDG must remain connected for at least 1.5 seconds
  • Above 80%: MSDG must remain connected indefinitely for voltages above 80% of nominal
  • Below boundary: MSDG may disconnect for voltage-time combinations below the red boundary

4.5 Frequency Response Capability

MSDG installations shall be capable of operating within the frequency ranges specified below and shall not trip due to normal frequency variations.

Figure 3: Frequency Response (Frequency vs Time)

FREQUENCY RESPONSE REQUIREMENTS

MSDG shall remain connected within the green shaded area

52.0 Hz
51.5 Hz
51.0 Hz
50.75 Hz
50.0 Hz
49.25 Hz
49.0 Hz
48.0 Hz
47.0 Hz
Frequency (Hz)
0
1s
2s
3s
10s
60s
Time (seconds)
Normal Range: 50.75 - 49.25 Hz (±1.5%) Emergency: 52-50.75 Hz Stay connected ≥ 3s Emergency: 49.25-47 Hz Stay connected ≥ 3s 50 Hz 52.0 Hz 47.0 Hz 3s @ 52 Hz 3s @ 47 Hz

Frequency Response Requirements:

  • Normal Range (50.75 - 49.25 Hz): MSDG must remain connected continuously (indefinitely)
  • Emergency Upper (52 - 50.75 Hz): MSDG must remain connected for at least 3 seconds
  • Emergency Lower (49.25 - 47 Hz): MSDG must remain connected for at least 3 seconds
  • Beyond Emergency Limits: MSDG may disconnect for frequencies outside 47-52 Hz range or after 3 seconds in emergency range
  • Rate of Change of Frequency (RoCoF): Loss of Mains protection set at 2.5 Hz/s or 10° Vector Shift, clearance 0.5s

4.6 Power Quality Requirements

Table 7: Harmonic Current Limits (Odd Harmonics)

Harmonic Order (h) Maximum Harmonic Current
(% of fundamental current)		 Applicable Standards
3 4.0% IEC 61000-3-2
IEEE 519
5 4.0%
7 4.0%
9 1.5%
11 ≤ h ≤ 15 2.0% IEC 61000-3-2
IEEE 519
17 ≤ h ≤ 21 1.5%
23 ≤ h ≤ 33 0.6%
h > 33 0.3%
Total Harmonic Distortion (THD) ≤ 5.0% IEC 61000-3-2

Table 8: Harmonic Current Limits (Even Harmonics)

Harmonic Order (h) Maximum Harmonic Current
(% of fundamental current)		 Applicable Standards
2 1.0% IEC 61000-3-2
IEEE 519
4 ≤ h ≤ 10 1.0%
h > 10 0.5%

Additional Power Quality Requirements

Parameter Limit Standard
DC Current Injection ≤ 0.5% of rated current IEC 62116
Voltage Unbalance (caused by MSDG) ≤ 2% IEC 61000-3-13
Flicker Severity (Pst) ≤ 1.0 IEC 61000-4-15
Flicker Severity (Plt) ≤ 0.65 IEC 61000-4-15
Power Factor at Point of Connection ≥ 0.95 (leading or lagging) Grid Code Section 4.2

Notes on Power Quality:

  1. Harmonic limits apply at the Point of Common Coupling (PCC) - Point A in Annex 6.
  2. Measurements shall be taken under rated power conditions.
  3. For multiple MSDG units at the same location, the combined harmonic contribution shall not exceed the limits.
  4. The MSDG owner is responsible for installing harmonic filters if necessary to meet these limits.
  5. Power quality measurements shall be conducted during commissioning and annually thereafter.
  6. Non-compliance with power quality limits may result in mandatory disconnection until remedial measures are implemented.

Compliance Testing

Required Tests:

  • Fault Ride Through Test: Verify MSDG remains connected per Figure 2 requirements
  • Frequency Response Test: Verify MSDG remains connected per Figure 3 requirements
  • Harmonic Analysis: Measure and verify compliance with Tables 7 & 8
  • Power Quality Assessment: Full power quality study including voltage, current, harmonics, flicker
  • Protection Settings Verification: Confirm all settings align with operating characteristic requirements

Refer to Chapter 5 for detailed testing and commissioning procedures.

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