1. Introduction With the adoption of single-chip microcomputer technology in relay protection, many concepts should be updated. Unfortunately, some concepts based on the mechanical protection era remain unchanged, failing to fully utilize the advantages of microcomputer protection. This article will explore these issues using several basic types of protection as examples, hoping to stimulate further discussion and welcome valuable feedback from colleagues. 2. Low-Voltage Busbar Protection Busbar protection is installed on the busbars of substations. In the event of a busbar fault, it quickly disconnects the fault, meeting the requirements for safe operation of the power system. Currently, the principle of busbar protection mainly uses current differential protection, connecting the secondary currents of all outgoing lines on the busbar to a centralized bus differential protection device. This wiring method involves large investment and complex wiring. This is especially true in low-voltage busbars. Traditionally, substation busbars are generally not protected, relying on the transformer's backup protection to trip the circuit breaker with a delay. This can lead to competition for the output with the opposite side's distance protection, causing the fault to spread and damaging primary equipment. With the introduction of network technology into substation automation, especially the multi-ID address feature of the CAN 2.0B protocol which makes point-to-point communication within the substation possible, the concept of networked low-voltage bus protection has emerged. Networked low-voltage bus protection collects protection action information from each 10kV outgoing line suspended on the bus via a CAN network bus. This information is analyzed and processed logically through a pre-set protection program: if any line protection action information is received, the low-voltage bus protection is blocked; if no line protection action information is received, the low-voltage bus protection is activated, the faulty bus segment is identified, and the associated circuit breakers of the faulty bus segment are quickly disconnected. This ensures that when a bus fault occurs, the fault point can be quickly located and the fault can be quickly disconnected within the minimum time limit, thereby ensuring the safe operation of the power grid and the reliability of power supply. The above solution has been granted a patent by the State Intellectual Property Office: Patent No. 00221250.1. 3. Small Grounding Current Detection Device Currently, small grounding current fault location devices in power systems generally use the direction of zero-sequence power, the magnitude of zero-sequence current, and the magnitude of zero-sequence voltage as the basis for determining whether a line is grounded. This device can only select once after the initial detection. However, when the system's zero-sequence current is very small, without obvious characteristic electrical quantities, it often makes incorrect judgments, failing to provide correct operational guidance to on-site operators, increasing the workload of on-site maintenance personnel, and failing to meet the requirements for rapid fault isolation, thus posing certain hazards to the site. Similarly, this device utilizes the network information of the substation's field CAN bus to obtain information such as the zero-sequence voltage, zero-sequence current, and direction of zero-sequence power for each line unit. Through a pre-set judgment program, it selects the line with the most obvious single-phase grounding fault characteristics in the small grounding current system and sends a trip command to that line via the network to trip it. Then, it continues to use network information characteristics to determine whether a grounding fault still exists. If a grounding fault still exists, it continues to send trip commands to the corresponding lines. The circuit with the most obvious existing fault characteristics is tripped, and a closing command is sent to close the circuit that was tripped the first time. This process is repeated three times until the fault disappears. The tripped circuit is the grounded circuit. This ensures that the grounding point can be quickly and accurately located when a single-phase grounding occurs in a low grounding current system, reducing maintenance and meeting the requirements of a power system for rapid fault isolation, thus ensuring the safe operation of the power grid and the reliability of power supply. The above scheme has been granted a patent by the State Intellectual Property Office: patent number 00221250.x. 4. Sensitivity Enhancement Method Without Phase B Current Transformer Traditional overcurrent protection uses the phase current method for operating current. 10kV line overcurrent protection generally only has two current transformers, usually providing A-phase and C-phase current. In traditional relay protection configurations, only A-phase and C-phase overcurrent relays are used. This reduces the sensitivity of the protection when a two-phase short circuit occurs after the transformer in a Y/Δ connection. A third relay, which would increase sensitivity by reacting to I_a and I_c, is often not installed due to cost considerations. This often leads to cascading tripping during an accident, expanding the scope of the power outage. In microprocessor-based protection, for three-phase short circuits, the phase current I is still used as the operating current of the overcurrent protection, that is, the operating criterion is I>Iset, where Iset is the operating setting value. Then, using the principle of three-phase current balance, the current of another phase is obtained from Ib = -Ia -Ic. Taking full advantage of the computability of microprocessor-based protection, an additional element for protection operation is added, and the two-phase three-element method of protection current is realized without increasing any hardware cost. This greatly increases the sensitivity of the protection and avoids the expansion of the power outage range due to accidents. 5. Sensitivity increase method with B-phase TA The traditional overcurrent protection operating current adopts the phase current setting method, which makes the sensitivity of three-phase short circuit 1.15 times that of two-phase short circuit (Z∑(1)=Z∑2). After the setting calculation, the sensitivity must be checked again, which is particularly inconvenient. In microcomputer protection, the computability of microcomputer protection can be fully utilized. After collecting the three-phase phase current, the phase current is transformed into line current through star-angle transformation, that is: Iab = Ia - Ib, Ibc = Ib - Ic, Ica = Ic - Ia. The line currents Iab, Ibc, and Ica are used as the operating currents of the overcurrent protection. When (Z∑(1) = Z∑2), the maximum line current of the two-phase short circuit and the three-phase short circuit are always equal. Therefore, the sensitivity of the three-phase short circuit and the two-phase short circuit are equal. The setting value and the sensitivity verification can be calculated only according to the three-phase short circuit, which greatly reduces the workload of the field personnel. In some traditional protections, such as overload alarm, overload blocking, on-load voltage regulation, and overload start-up air cooling, only the B-phase TA is often used. This is based on the reason that the A and C phase TAs are overloaded and that installing more relays will cause economic waste. In microprocessor-based protection systems, these two factors are completely absent. The AND gate output of the three-phase current discriminant I_a, I_b, I_c > I_set can be fully utilized, greatly increasing the reliability of the device. 6. Problems with Zero-Sequence Gap Protection In traditional relay protection, zero-sequence gap protection has always used ordinary overcurrent relays to achieve the protection function. However, in the field, the discharge gap often experiences a momentary discharge during overvoltage, followed by an immediate voltage drop, stopping the discharge abruptly, then a voltage rise, and the discharge begins again—a pulsed discharge process. Traditional relays cannot mimic this actual process and cannot achieve the most perfect protection effect. Microprocessor-based protection, with its memory and computational characteristics, can mimic the actual discharge gap process, accurately reflecting the fault situation and achieving better protection results.