The paper presents the methods of assessing the technical condition of varistor surge arresters used in laboratory tests and in operation—performed without disconnecting the arresters from the network. The analysis of the diagnostic methods was supplemented with the results of the measurements of the leakage current of arresters coming directly from their production and used in the power industry. Among the available methods of evaluating the technical condition of arresters, mainly indicator solutions (temperature and operation counter) and the measurement of the selected parameters of the leakage current are used. In the latter, the method of determining the resistive component of the leakage current, determined on the basis of the analysis of the voltage and current waveforms, or only the arrester current, has become widespread. In this type of measurement, current clamps are used in the operation, and additionally, in voltage measurements, voltage transformers are used, where you have to take into account the fundamental, additional sources of errors discussed in the article. These errors and the dispersion resulting from the production technology may fundamentally hinder the proper assessment of the technical condition; hence, it is so important to properly recognize the listed basic sources of measurement uncertainty. In addition, the analysis should take into account three factors related to external conditions: temperature, the voltage applied to the arrester, and the content of higher harmonics in the supply voltage, for which appropriate methods have been provided to determine the active component of the leakage current for reference conditions. This article presents the results of the measurements of the leakage currents of surge arresters measured with various methods.

New intermetallic compounds Tb ₂ Pd _1.25 Ge _2.75 and Dy ₂ Pd _1.25 Ge _2.75 have been synthesized using the arc-melting method. The crystallographic structure and magnetic, electronic transport, and thermal properties are reported. The crystal structure obtained from powder x-ray diffraction analysis suggests that these compounds crystallize in the AlB ₂ -type structure (space group P6/ mmm , no. 191) with lattice parameters a = 4.228 53(5)/4.230 54 (2) Å and c = 3.942 25(9)/3.945 52(5) Å for the compounds with Tb and Dy respectively. The ac and dc magnetic susceptibility studies reveal spin-glass like behavior, with freezing temperature T _f = 10.5 K for Tb ₂ Pd _1.25 Ge _2.75 and 4.5 K for Dy ₂ Pd _1.25 Ge _2.75 . These data are in good agreement with the heat capacity measurements.

The intermetallic germanide ${\mathrm{Gd}}_2{\mathrm{Pt}}_{1.1}{\mathrm{Ge}}_{2.9}$ was synthesized using an arc-melting method. The crystal structure was characterized using powder x-ray diffraction, revealing a disordered ternary ${\mathrm{AlB}}_2$-type structure (space group $P6/mmm$, No. 191) with lattice parameters $a=4.2092\left(1\right)\AA$ and $c=4.0546\left(2\right)\AA$. Physical properties were investigated by magnetic susceptibility and heat capacity measurements, which indicated onset of antiferromagnetic order at $T_t=8\mathrm{K}$. The obtained properties were compared with the ones reported for other members of the ${\mathrm{AlB}}_2$-type ${\mathrm{Gd}}_{2}T{\mathrm{Ge}}_3$ ($T=\mathrm{Ni}$, Cu, and Pd) family. The magnetic ordering in these compounds was discussed in terms of their crystal structure and the influence of Gd ions.

Two new ternary germanides Tb₂Pt_1.2Ge_2.8, Dy₂Pt_1.15Ge_2.85 and one already known germanium Ho₂Pt_1.1Ge_2.9.were synthesized using an arc melting technique. The obtained samples were investigated by powder x-ray diffraction, which indicated that all of them crystallized in a hexagonal structure with P6/mmm (no. 191) space group. This structure is a disordered variant of the AlB₂ aristotype that favors the formation of a spin-glass-like state. The physical properties were examined by measuring magnetic susceptibility, heat capacity and electrical resistance. Experiments indicated that all of the compounds can be classified as cluster-spin-glasses with the freezing temperature of T _f = 12.0 K, T _f = 6.0 K and T _f = 2.9 K for Tb₂Pt_1.2Ge_2.8, Dy₂Pt_1.15Ge_2.85 and Ho₂Pt_1.1Ge_2.9 respectively.

Users expect reliable operation of the surge arrester during overvoltages, which may originate from a switching process or a lightning discharge. The necessary conditions to guarantee these expectations are: appropriate construction of the surge arrester, its production being maintained in accordance with technical standards, and a positive results of the type test. The recipient, especially when purchasing large quantities of the product, can check the final quality of the product through selective testing of samples from the market in order to find the best supplier. This manuscript specifies the basic parameters of low-voltage (LV) surge arresters of four manufacturers. Basic electrical parameters, i.e. leakage current and reference voltage before and after the discharge current of 8 μs /20 μs, were determined for 10 randomly selected surge arresters of each manufacturer. Moreover one sample of each varistor batches was aged by 50 simulated lightning strikes. The obtained results of structural analysis indicate that the crystal structure of the varistor materials changes after ageing process, affecting its electrical properties. The proposed research methodology can be employed as a basis for forecasting the stability of the arrester parameters under operating conditions.